Even for the early '80s, when there was a glut of lurid posters to be found, this was a repulsive piece of work. Try to imagine seeing this elegant art hanging in any theater lobby today. It just wouldn't happen because from top to bottom, everything about it is so wrong.
If I had to single out the most offensive aspect of this poster, though, it wouldn't be the bloody knife, or the woman's scalp held in the killer's hand, or even the glimpse of the killer's fat, hairy gut showing through the gaps in his unbuttoned shirt. No, I think the most appalling sight by a mile is the huge fucking bulge in the killer's jeans.
Apparently having the knife held directly over the killer's crotch wasn't an obvious enough phallic symbol. Hell, no - they had to get the actual dick in there, too, just so no one would not know that killing gives this guy a massive hard-on.
When Maniac was originally in theaters, offended women's groups painted over this poster and even though I don't support censorship, it's easy to understand the outrage. When it comes to horror movie posters, there's everything else and then there's Maniac. Whatever you say about it, you can't say that it was soft.