I haven't worked enough for this to ever have become an issue. Well, okay, that's not entirely true. One lady said I'm not a very good employee (or whatever she called me) when I worked a temp job for Miami Herald customer service because the only information they gave us was a little pamphlet and I didn't know the answer to her question. I'm honest and extremely bad at bullshitting so I just told her, "I don't know."
Another time I was working at a car wash and someone asked me if I'd dried a particular part of the car (the door frame at the bottom) and I didn't remember and I panicked and said yes (I should have just said I wasn't sure, but I felt like I didn't have time to think). It turned out it was still wet, and the owner yelled at me that I wasn't "doing a good job today." The shape of her lips was kind of absurd, she looked like one of those dolls that are made to accept a bottle in their mouths. I had half a mind to tell her, "you look like you breastfed for way too long," but a higher part of my brain suspected that wouldn't have very good consequences regarding my employment there, so I didn't. (A minute later she said she was just frustrated.)