You're not in a good position to be engaging in fisticuffs while sitting on a motorbike. If someone grabs your hand you can't do much with the other one, and one good shove and you'll be over. Plus, you need both your hands and feet to operate the controls while the car driver could, while still gripping your hand, engage gear with the other and drive forward, dragging you over. It's unlikely as they would worry about getting their paintwork scratched, but if they're in an older car it's something to be aware of. At best you'd end up with a Mexican stand off.
On the other hand, if you get off your bike even the wimpiest biker must look like the Terminator when standing glaring through the driver's window. It's one thing disrespecting more vulnerable road users when you think you can get away from them but if you're confronted with an irate armoured individual when you're stuck in traffic it's quite a different thing. I've been told I look quite scary (What! Mild mannered me?) but I suppose I don't think about it much as I'm a bit old school, out on my old school Honda pretty much every day. I always think that they can't hit you if you're not there, and try to keep out of such situations in the first place, and the same when out cycling.