Renegade Female Shepard.
No, seriously. This is the first thought I had when answering this poll. Actions are definitely unexpected at times, more than a little bad ass (thanks to Jennifer Hale's talent), and, most importantly, a great source of the lulz.
And thinking about it more, really those are the moments I remember most in RPGs. From the option in KOTOR II by dealing with NPCs in Nar Shadda by having them jump over the railing (via Force), or your random Shepard's punching/head butting/collar grabbing antics, it's always good for a laugh.