I didn't realize "yeahno" was widespread. It must have been from Friends, that show was pretty popular.
hehe... awesome thread. 
My saying that has people looking at me as if I was a square egg is "same difference."
I like that one actually!
Here's something else I've noticed, I think I've traced it to a particular friend but maybe it's widespread: saying "I dunno" before everything.
"How was your weekend vacation?"
"I dunno, it was good we went waterskiing"
"Hey what's up?"
"I dunno, we're all at Tim's watching the game"
"Wanna come play some tennis?"
"I dunno... No, yeah, sure I'll come"