I've never really had any trouble as I've been a fairly popular dude since like year 5. Only two times I've had a problem of sorts was in year 7 getting beat up by the big kids at the back of the bus, but they beat everyone in year 7 up, so I wasn't really being picked on and it's actually quite funny in retrospect.
As for the second time, in secondary school I decided to grow my hair long, which was cool beans because like I said, I never had a problem with anyone. Although briefly, when I was in year 11, afew chavs who didn't know me in year 10 tried to start because they thought I was a hippie or something, so one of them starts on me thinking I'm gunna be all like scared and shit, so I slap him about about, throw him on floor and he gets real shaken up saying stuff like 'Mate, I was just joking wtf?!', then they got scared and ran off with their aunt and uncle in Bel Air.
But yea, I've always been well liked and scary looking so never got much trouble, although growing your hair is a sure fire way to get some randomers start.