Either report him to any server admins, or find a way to trap him.
SMP help

there are a few ways with redstone, constant movement traps mixed with obsidian and an elder guardian.
The hardest thing would be getting him in position, but if he is hunting you, that makes it much easier.

dig down to bedrock, then add powered snow in a single layer by his bed. He will spawn on the snow, break it, and cause his own death. Keep his bed with slabs or blocks above it, so he can't spawn on it.

I play on this SMP at school and there is this person that is trying to kill me. He succeeds sometimes but im usually able to kill him easily. Hes just being mad annoying. what should I do for revenge?
if you want to be smart, just trap his spawn or go far away yourself. If you want to be upfront, do something that will show him your dominance and he'll leave you alone
I play on this SMP at school and there is this person that is trying to kill me. He succeeds sometimes but im usually able to kill him easily. Hes just being mad annoying. what should I do for revenge?