I used to be the same, but this is what I did - think about what's the worst that could happen. You take a couple of punches, maybe your nose or mouth hurts for a few days afterwards, and then what? Nothing. It's no big deal. The more and more confident you portray yourself as being, and the more and more you learn about a martial art/combat sport, the less likely this is to happen anyway.

DO not be afraid, with fear comes weakness, what is there to be scared about? just ask yourself that, you will find most big mean are nice guys, if not you neeed to believe that in a physical confrontation, you would win. How could you lose? haha you are a bad *** mother trucker. alternatively, go to the gym, bulk up, or learn to fight, that is what helped me when i was in your situation, i leanr martial arts and studied fighting, noone knows it and they still attempt to pick on mt sometimes but.. if it got physical, it would be over.. pretty fast, it helped, me it could help you :)

Practice boxing. You might find out you have good power to knock people out. Musclemen mostly don't have power to hit hard and dies in 2 rounds.

learn some martial art

I'm scared of people who pick on me and scared of big muscle men. Hate going to crowded places.

My grandad says I should man up and don't be scared of anyone, they're like you, human.

Have heart, muscles don't matter, is he right?

What's heart?