zombie pigmen are not fair they start attacking the player after they killed a mob that attacked one of them

If you spawn more than one zombie pigman and spawn a ranged attack mob(such as skeleton)
and stand behind one of the pigman the skeleton will shoot that pigman and they will start killing the skeleton and when they finish they will start attacking you without any reason!

and if you die they will keep attacking you in case you respawned and went to them.