When I've run out of things to say I just go "meh", "shpleh" or "meauugh". Unfortunately this is usually the cue for a victory dance on the other side of the argument. I also wave my finger and go "Nimnimnimnimnim" to get the other side of the argument's attention while I try and form sentences.
Another really odd verbal tic is the explaining voice. Everyone has one (tiny children all have the same one), but mine is a really broad accent of some description. "Ye getcher x, an ye times it by y, an then, ooo, that's where me muffin went, but ye gotta flip it round liike so, an then ye gotcher solyution."
I also refer to people as "it" or "that". It started off as a friendly insult and is now a full-blown verbal tic. Crazy world.