A, Uhm
A mix of 'uh' and 'um' used when you're talking to someone who's so dumb they make you want to scream.
A: Why is the sky green? B: Uhm... because you're a dumbass.
A: What's your name? B: Uhm... I don't know, you tell me.
A: Why are you crying? B: Uhm... I'm not sure, maybe I just peed my pants.