Andersp:  I've always thought it was bad manners to drag out a game that was mathematically lost.  But of course, if an opponent asks me to let the game finish, I will.

Etiquette, after all, is just a default set of rules to follow until you understand each other well enough to know what will offend and what will not.  It's not a substitute for friendship, but just something to smooth the path while friendship and camaraderie develop.