What do you say if you want to tip a specific amount when paying in cash?
Say I've had a small meal for $8 and want to tip $2 on top of that. If I have a $10 bill, I'd say "keep the change" (By the way, should that be "keep the change, please"? Or "you can keep the change"?)
But what if I only have a $20 bill? Would I say "give me back $10, please"? That could quickly get tedious with larger amounts. Or something like "and a $2 tip"? "Two of those are for you"?
I'm sure I'd get the point across, but anything I can think of sounds convoluted or patronizing. When I hear "this is for you" I think of my grandmother giving me some money behind my parents' back...