So Im looking for a manga with an evil seme in a sense. This is a very vague description.. sorry

I try to stay away from nasty protagonists, but I remember that Fujimoto Haruki's Final Impression had a pretty mean seme.

By mean streak, do you mean in general or in the way he treats the uke?

Kinda both, just an unpleasant person in general

Otona Keikenchi - the balance between mean and loving is nice.

Sono Kuchibiru ni Yoru no Tsuyu - they both have mean streaks...

I recommend the Character Who Bullies the One They Love category if you haven't already tried it.

Bi no Isu maybe.
Zion no Koeda
Devil x Devil
Koibito wa Hatsujouki

That's all I can think for now. I'll come up with more later though
🙂