Only once. A rager got out of his car and tried to punch me. Luckily he missed as I dismounted. he then tried to grab me, where upon I remembered a self defense lesson from when I was about 13 and I shoved my fingers under his adams apple and shoved in and up, causing him to almost throw up and release me. He then thought better of it and walked away without saying a word. Whole thing took about 15secs from start to finish, we didn't even have time to exchange insults. To this day I'm not sure why he decided to target me, I can't remember even having an altercation in any way.
Anyway I got the better of the exchange and no-one was seriously hurt (apart from his pride I'd imagine)