My brother is on the right dressed as Frankenstein's monster.
I'm on the left and as I was scanning this photo I realized that I had no idea who I was supposed to be. Turns out that The Red Skull was, depending on which era in the Marvel Comics Universe he appears, either a nazi personally trained by Hitler or a communist spy and imposter. One version of the character was responsible for the deaths of Peter Parker's parents and thus intitiated the creation of Spider Man.
This photo was likely taken by my grandmother (which would make that her finger visible on the left) since we're in her dining room in front of her cuckoo clock. If her or my grandfather, a WWII veteran, had known anything about the nature of The Red Skull I imagine they might have berated my mother and ordered me out of the costume immediately.
For myself, all I can imagine is that I had seen the costume in a store and thought, "ooh, that looks scary." Until today I had no idea what a disturbing character I had chosen to emulate.