Costco employees reveal the worst, grossest, and most bizarre things they've seen on the job

"Someone pooped on the floor in the clothing department and tracked it all the way to the bathroom," said one Costco employee based in Chicago.

"A guy fell through our roof," a Costco employee from Oregon told Business Insider. "He was working on the roof, sat down on the edge and somehow fell backwards. That’s why now Costco requires bars on the sun roofs."

A Costco employee who's worked at the chain for eight years once encountered "a 60-year old woman who threw an actual tantrum because we refused to return her stained, eight-year-old mattress."

A Costco employee from Illinois reported witnessing members successfully return dead trees and plants to the store.

A Costco worker from Arizona once saw "a lady leave her baby inside her car on a hot summer day."

"An older gentleman cancelled his membership because state law requires that we tax an item based on the pre-coupon price," a Costco employee from Minnesota said. "When we didn't 'fix' it to save him about a dollar, he decided he never wanted to shop at Costco again."

A Costco employee in Washington reported witnessing "people sneaking their animals in." In some instances, the worker added that the pets have proceeded to "defecate on the floor."

"A woman came in and returned two dirty toilets that she had purchased online over five years ago," a Costco worker who's been with the chain for three years told Business Insider. "She 'didn't need them anymore.' She didn't even clean them! I'm embarrassed that we ended up taking them back, but we did make her take them outside and clean them before we did."

A Costco worker in Nebraska said they had seen members' children running around the store and parking lot in the dead of winter "with summer clothes or no shoes on."

"The worst is people returning perishable food because they 'bought the wrong thing,' 'overbought for our party,' 'bought on impulse'' and other reasons that have nothing to do with dissatisfaction with a product," a Kentucky-based employee told Business Insider. "We end up having to throw the food away because it can't be resold if it left the building."

A Costco employee in San Francisco said they had witnessed a lot of members getting chased down for shoplifting, saying, "A lot of people try to come in and steal and get caught for it."

A Ohio-based Costco worker said they once saw a member "trying to return a 10-year-old vacuum."

"I've seen a member pull out a gun and threaten to shoot another member," a Florida-based Costco worker told Business Insider. "This was a disagreement over who was going to park in a handicap spot."

"The craziest thing I've seen working at Costco is a part-time member service employee enter the food court and make out with the food court manager after the warehouse was open," a Costco employee of seven years told Business Insider.

A Nebraska-based Costco employee reported seeing "people stealing underwear and leaving the old ones behind."

A Costco employee from Illinois described seeing members attempting to return "all eaten pies or baked goods" and claiming they hadn't liked them.

"I've seen people arrested, convulsing, hemorrhaging, screaming," an Arizona-based Costco worker told Business Insider. "And a few loose animals running through the store."