My "favorite" thing is to have something that comes up to some amount of dollars & cents like $1.27 and then hand them $2.02 and watch the gears turn and get stuck... "Uhh... it's 27 cents, not 2..." "Just key it in and see what happens..." "But it's 27 cents..." "Just do it, please..." "Oh, you get 75 cents back?!?!?" Heaven forbid the register is non-functional.

How about prices that are intended to be 25 cents, but are listed in the form of "0.25 cents"? I try to explain to folks that the sign should be "$0.25" and that the way it's written means I could get four for one penny. They'll usually say something like "No, it's point two five cents each, not four for one penny..." Not too long ago, I was going to buy some free weights and saw that they were listed as "0.45 cents per pound" and tried to explain it to the dolt and bimbo working there, but they didn't get it and said the manager would have to figure it out (the next day). I told them I'd be back then (I couldn't transport them that day anyhow) and that if it wasn't fixed, I'd demand the price as it was written. The manager was not so clueless and had the price fixed, but gave me a break because of the error.

On the "supply" side, I worked at a local tire shop and at Pep Boys during college and a bit afterwards while waiting to go on active duty -- I met PLENTY of clueless folks both in the customer and employee populations. One guy came in to the flea market location of the tire shop I worked for...

I have many more tales of cluelessness, but my "diary" of them is at home...