Being an American, I usually just hack British slang that makes it's way over across the pond: Cheeky, chuffed to bits, chin wag, wanker, etc. I have a grand time trying to work the word "Trebuchet" into conversation...my girlfriend loves it when I pull it off, just makes her giggle. But yeah...I think a good vocab, especially one that American ears don't get to hear a lot of unless they're ardent listeners to the BBC or Radio 1 or whatnot makes the speaker (i.e., me) seem darned clever... I also use a lot of words on the east coast that I picked up growing up in the midwest: Onery, yonder, tarred out, etc.