My new pet peeve today is people who ASSUME the change is theirs to keep... for a tip.
Last weekend I was at a restaurant with a few people (7 I think) and we each got our tickets and send our payments back with the waiter. One of us (not me) paid cash. His bill was $11 and some change and he'd give a $20 bill. When the tickets came back for us to sign (credit cards) or our change, he didn't get change. The waiter said he'd kept it for a tip! Our buddy laughed hysterically and said he wanted ALL of his change and there was no way he was going to tip almost as much as his bill was! It was rude of the waiter to assume the change was his.
Well today at Sonic the little carhop chick kept my change without me telling her to. I know it was happy hour and my coke was only 81 cents... and I gave her a $1, but still to just grab it and barely spit out a thank you and not even act like you thought about change. Took it and ran! That pisses me off. If she'd offered me the change, i'd said 'keep it'... but now that you take it and run, i'll be SURE to only give you exact change next time!