The best gimmicks are extensions of yourself, or your real personality amplified. Check out this video of Dean Ambrose "out of character":
The lack of eye contact, the swaying, the creepy speech cadence, heavily emasculating that gum, the crossed arms indicating he's slightly uncomfortable with it all...this dude is slightly off, and gives off that vibe that you get from an actor who takes method acting a bit too seriously and people whisper about being eccentric.
He's really a fascinating dude with real creepy charisma.