I commented on this over on Toronto Mike.com, who was complaining about tiny coffee cups often found at breakfast diners. I have a related irritant regarding tiny diner coffee cups.
Maybe I'm labelled a pain in the ass by servers who attend to me, but I always prefer a fresh, clean cup when they come around to refill your coffee. In other words, don't pour fresh coffee over the few remaining ounces of cooling coffee in my cup. Servers will often come by and say "would you like me to warm that up for you?" Um, no..no I don't want that hellish alchemy at all thank you very much.
If I'm at a bar and my pint is nearly done, the bartender doesn't say "would you like me to cool that down for you?" and pour new beer over the old beer. If he or she does, that tells me there's an excellent chance I'm getting knifed at that bar.