Oh well that's not what a smart mouth entails but I understand your point now. Ryan Reynolds I think is plenty tough after seeing him in Smoking Aces, The Amityville Horror, and Blade Trinity, though. Dane Cook I wouldn't know about since he's only done comedic roles but I don't see why he wouldn't be able to pull it off with a good crew behind him.
I can't remember the name of the movie but Cook was in it and he played a serious role(well it wasn't a comedy)...I think he was a crazy insane guy or something. Idk i didn't see it but I guess one could look there to see if he can act tough and crazy.