A little story: last year, every time I took my shirt off in PE, I got whipped by about 5 or 6 belts from fellow classmates. One day I took off my belt before my shirt and screaming ensued. They didn't do it again

Not really bullying though, because we're all mates in PE.
Bullies: serious stuff. They're people who make you feel unpleasant over a long period of time (read: not just they once did something bad to you)
Solution: kick em in the crotch or get a friend to do it if you want to be plain about it.