I'm a wedding planner. Here are 12 common mistakes I see guests make.

• I'm a professional wedding planner, and I've seen plenty of bad guest behavior at events.
• It is your responsibility to RSVP, show up on time, and keep track of your things at a wedding.

In my five years as a professional wedding planner, I've learned a thing or two about the people who attend my events.

Read on for the most common mistakes I see wedding guests make, and how to avoid them.

Please don't wait until the last minute or forget to RSVP

A wedding isn't like a normal party where you can see how you feel in the morning and decide accordingly.

The event often involves catering, whether it's a backyard potluck or a formal dinner, and whoever's providing the food must know how many people to plan for.

When you refuse to RSVP, you force the couple to track down the information when they're already way too busy trying to plan their wedding.

Don't act like you know the couple better than they know themselves

Wedding planning can take its toll, but most people getting married still know their own minds. They are, after all, adult humans.

Believe them when they tell you what they do or don't want.

This push-and-pull often comes up around registries. If the couple asks for cash, donations to nonprofits, or non-physical gifts like gift cards or experiences, please don't tell them they're wrong and buy them a vase.

The best gift you can give as a guest is respecting their wishes.

Vendors are there to make the event run smoothly — don't make their job harder by being rude

Wedding vendors build their businesses on serving others, but that doesn't mean you should take advantage of them.

Guests often forget this, particularly after a few trips to the bar, but don't make a fool of yourself by snapping your fingers at the caterer, telling the florist how to do their job, or cornering the wedding planner.

Treat the vendors like you would want to be treated if you were working a physically demanding, often underpaid service job.

Speak up if you're nervous about attending the wedding for whatever reason

In some situations, wedding guests need certain things in order to feel safe while celebrating the happy couple.

Guests may need information about a venue's accessibility, confirmation that the food won't cause an allergic reaction and/or violate a religious belief, space to breastfeed, details about the wedding's COVID-19 safety policy, or assurance that they won't be at risk because of their race or sexual identity, to name a few.

In an ideal world, the couple will proactively provide this information, but wedding planning is easily a 10-hour-a-week commitment, so some things fall through the cracks.

If you need something from the couple, please tell them with kindness, empathy, and as much notice as possible. They want you to enjoy yourself as much as possible — it's why they invited you in the first place.

The couple didn't hand-pick favors for you to leave them on the table

I know none of us need more monogrammed knickknacks, but just grab the darn coozie, OK?

You can toss it or, ideally, recycle it as soon as you get home, but if you leave it at the wedding, you're just giving the couple more to clean up.

And a tip for couples: If you give favors, try to make them something that won't end up in a landfill.

Before you reach out to the couple with a question, read what they sent you

As a guest, you've likely received at least one piece of correspondence from the couple. Often it's a save-the-date or an invite, but sometimes it's a wedding website, Facebook group, BCC'd email, or very long text thread.

Whatever the medium, please do the reading.

Those messages contain vital information about the wedding — most critically, they'll detail when the ceremony starts. Don't be the guest who asks the couple for this information the night before the wedding, as nearly all couples tell me at least one person did before theirs.

You're in charge of keeping track of your personal belongings at a wedding

It never fails to amaze me what a wedding guest will leave out for anyone to grab — purses, cell phones, credit cards. I've seen it all sprawled out on a table as the guest dances the night away.

This advice isn't to scare you into thinking someone's going to steal your stuff. I've never had this happen in the more than 50 weddings I've planned. A wedding vendor has a lot more to lose than a guest if they're accused of theft (i.e. their entire online reputation and livelihood).

But please try to remember where you put your stuff. A good place is on your seat. Tuck that seat under the table or put something over the items and then let loose.

It's much easier to reclaim these items — or, as often happens, have a sober vendor help you reclaim them — if we can narrow down where you've been.

Do yourself a favor and pack a snack so you don't get hangry

This sounds silly but seriously, throw a granola bar in your bag or stuff a few fruit snacks in the glove compartment.

The biggest complaint I hear from guests is that they're hungry, and although I agree that the best parties have plenty of good food, sometimes a couple literally can't afford to give you the five-course meal of your dreams.

Don't spend the day hangry — pack a few back-up snacks just in case.

If you're buying a big or heavy gift, just mail it to the couple

I love the statement you're trying to make with that giant, 50-pound present. Gift-giving is clearly how you express love, and I'm here for it.

But what the heck is the couple supposed to do with that at the end of the night?

Please make it easy and have big gifts mailed to the couple directly. If you feel odd coming empty-handed to a wedding, bring a card. Bonus points if you use the card to tell the couple what you sent them.

In nearly all situations, anything that's brought to a wedding must be removed the same day. That means your love token just became the problem of whichever VIP guest was tasked with clean-up.

Don't forget to factor in travel and parking time before the ceremony

It's a myth that weddings never start on time.

They can run behind, of course, but often there's so much programming after the ceremony that it's imperative the main event begins as scheduled, so you don't run out of time and get kicked out of the venue.

A guest's role here is to factor in travel time and parking.

This information may be readily accessible on the invitation. But if it's not, you have Google. Use it.

Remember, the wedding isn't about you

The purpose of a wedding isn't to spend the most money, wear the nicest clothes, or eat the best food.

The goal of a wedding is to start a marriage, so challenge yourself to center the couple.

Ask yourself if your complaint helps the couple accomplish their goal. If not, try to keep it to yourself.

Odds are you're not going to totally screw up the day, so stop acting weird

Guests have asked me enough dumb questions in five years that I've started to wonder what makes kind, intelligent people who seemed perfectly normal act so strange during weddings.

In my professional opinion, the weird behavior is nearly always the result of them thinking they're going to mess up the wedding. And the more they care about the people getting married, the weirder they get.

Consider this a pardon from an expert: You're not going to mess up the wedding unless you go after the couple's relationship. Not planning on doing that? Great, have fun.