Among those that offer just such a mask and that probable type of response are mass murderer Hannibal Lector, Meateater, and Chopper the Clown; all of which provide plenty of evil and scare when worn as a mask.
With Hannibal Lector, it's the motorcycle mask that covers the lower half of his face that we'll look at first. As you can see, it's an awesome mask to wear, especially when looking at that mouth area which appears so ominous. Add the right makeup to the eyes and you'll have a great, evil look for the party.
Next we have Chopper the Clown with that evil face that always seems to have that look that makes it appear he has recently taken a bite out of someone. The furrowed brow; large, sharp teeth; and the large red lips all provide that face that most of us have no desire to ever meet.
While all of these are great, evil Halloween masks, my favorite is this one of Meateater, which has that very realistic look to his face, especially the lower part on the lips and teeth. And how about those terrifying eyes? Wouldn't it be fun to walk up to someone unexpectedly and have them face you wearing this. Even the veins in the head look realistic.