Like when I am checking out and the cashier sneezes/ coughs on the item I am purchasing. Or when they are eating, sticking their fingers in their mouth, and touching everything! :O
A month or so ago I was purchasing a few needed items at a large retail store of Walls, and I approached the cashier pleasantly enough. As I mentioned, I work in retail too, so I'm as pleasant to them as I would like customers to be to me. After the initial greet, she pops a few...candies? Into her mouth. I think they were Skittles or M&M's, I don't know for sure, didn't want to peer into her mouth. However I very much dislike when people smack in front of me. Or chew like a cow. And talk with food in their mouth.
She rings up my items with fingers that recently were in her mouth, smacking away, and tells me the price. I pay with my card, take my bag, and leave. Upon inspecting the items in my car, I discover they're slightly sticky. Her grubby hands left a mark! Nothing some soap and water can't fix, but still. That's just nasty.