Is it harmful to my dick if i wear briefs high because i like that position.
It shouldn't be harmful. If you get an erection things can get tight, but in a flaccid state, you can wear it as high/low as you want.
Well, not to your dick, but it could limit sperm production in your testicles if your underwear is forcing them up closer to your body all the time, because of too much body heat (sperm production is optimum several degrees cooler than body temp). But, unless you're trying to get a lady pregnant, don't worry about it.