"Quit letting your kids jump around in the basket," an Iowa-based Costco employee told Business Insider. "It's dangerous."
Three other Costco employees added that they'd get nervous when parents allowed their kids to stand or sit in carts.
Another Costco employee from Illinois also said that too many people let their children "run wild" in the store.
Business Insider spoke with nine Costco employees who said they cringed when customers exhibited certain unhygienic behaviors, like putting membership or credit cards in their mouth or bra or failing to wash their hands in the restroom.
An Illinois-based Costco employee said they hated "... when they pull their card out of their bra or mouth."
"It's gross," said a Costco employee in Minnesota, while an employee in Idaho said this especially becomes a problem during "flu season."
"I hate when they have their membership card in their mouth and then hand it to me," a Ohio-based Costco employee told Business Insider. "Ew."
An employee in Chicago said they judged people who left the store's restroom without washing their hands, adding, "That's disgusting."
Two employees in Illinois and Ontario specifically called out people who cough and sneeze all over the warehouse without making an attempt to cover their mouths.
Behaving badly at checkout
Seven Costco employees told Business Insider that they judged members who hold up the checkout or membership signup line.
Three employees specifically mentioned how some people talk on the phone, which they said slows everything down.
"It's so rude," said one Ohio-based Costco employee, of people who hold extended phone conversations while checking in with the membership desk. "I've gotten to the point where I will tell people I will wait until they are finished, because I can tell they are busy. Then I take the next member in line."
Three employees also said they judged members who make no effort to help unload their carts.
Making the same old joke
A Minnesota-based Costco employee said they cringed when members joke around about how products "should be free" after they fail to scan.
Seven Costco employees told Business Insider that they judged shoppers who leave behind a trail of garbage as they move through the store.
One Idaho-based employee said they didn't appreciate it when people leave trash in their carts, while an employee in Ohio said people "leave their sample cups everywhere" and "spill their food and don’t clean it up."
"I work in the produce area and I can't tell you how gross and frustrating it is to find cups of soup spilled all over the product," an Ontario-based employee told Business Insider.
Leaving items in the wrong place
A total of eight employees from Costcos around the country described having an issue with members picking up items and then discarding them around the warehouse.
Especially cold items that would spoil after being left out.
One California-based Costco employee described members leaving "sandwiches under clothing tables." Another employee said people sometimes "leave frozen food items they decided they don't want in sundries."
A different Costco employee in California told Business Insider that it's much better to tell "the cashier you don't wish to purchase the item."
"If you are too lazy to walk it back, give it to an employee up front so the food doesn't go to waste," an Arizona-based employee told Business Insider.
An employee in Arizona also said they judged people who "open packages and decide to purchase an unopened one."
And a Washington-based Costco employees said they got annoyed when people "dismantled produce pallets because they think the freshest product is on the bottom."
Making ridiculous returns
A Costco employee based in Illinois said they judged people who "return things that are clearly from 2001."
A San Diego-based Costco employee told Business Insider that they judged members who start physical fights in the store.
Another employee from Illinois said they didn't appreciate it when members "... push past you without saying, 'Excuse me.'"
Bringing pets inside for no reason
A Costco employee in Hawaii said that while they understood some people rely on service animals, they resented members who bring in pets without cause.
"Allergies are real, and those of us who have them are adult enough to understand the need for service dogs," the employee said, adding that employees and members shouldn't have "to put up with your pet."
A Costco employee in Nebraska said they cringed "... when grown adults come in with their parents and make mom and dad pay for the shopping."
Leaving carts all over
"Members leave their carts on the islands and curbs instead of walking them to a corral," a Florida-based Costco employee told Business Insider. "I don't understand how they can walk around the whole store — which is pretty big — but suddenly be too exhausted to have manners and just return the cart. It's empty, so it's easier to push now."
An Arizona-based employee also said they judged people for " leaving carts in random places in the parking lot."
Misbehaving while getting a free sample
An employee in Arizona said they disapproved of people "blocking and grabbing the sample food like they have never eaten before."
Driving recklessly in the parking lot
A Costco employee from Ontario said they "hate" how members drive.
"Our parking lots are maybe the most chaotic in the country," the employee said. "I see at least three fender benders a month in our parking lots."
Touching people without their permission
One Costco employee from Oregon said they didn't appreciate it when members "... seem to think they can touch you. Or hug you... I don't mind the hugs, but at least ask."