I'm not the type to run away from a fight but... if I can give one piece of advice to anyone thinking of testing another person's self-defense skills... unless you have a gun (in which case you'll flash it before you use it) or have a black belt in any martial art (in which case you'll avoid defending yourself until the very end) I would NOT test the odds.
And weight IS NOT an issue. Any martial arts person knows that, regardless of weight, the other person has weak points (testicles,eyes, et cetera), and they know when and how to go for them.
Like I said, stick to the punching bag.