People making noises at the gore scenes in the cinema
I mean is it really necessary? Fine if it's just an involuntary gasp (like laughing during a comedy), but do you need to go "UURRRRGHHHHHH GROOSSSS MAN" at the top of your voice and then proceed to whisper about it for five minutes after?
It's no less acceptable than talking during a film. And don't bring your girlfriend if she can't handle it and has to keep whispering to you about it to diffuse her anxiety.