is it a sin to do bad things to your enemies? [Spirituality & Religion]

Revenge requires too much energy to be wasted on an enemy. Improvement of self is a better use of your energy and a stronger you, usually ends up leaving your enemy rather defenseless.

if you take these things into account by yourself then they are void on Judgement day , just a thought

I prefer not to have any enemies. I try to be friends with everybody.

No. It is what enemies are for.