Big Forehead Avalanche

Alright, listen up, you big-brained genius! This joke is basically making fun of someone's forehead. See, a "big forehead" is the target here. The joke then wildly exaggerates it by saying it's so massive, it could cause an "avalanche." That's already pretty mean, but then it goes full absurdity, connecting it to why "snow was found on Mars." Get it? Because your forehead is so huge, it's like a whole planet, or at least a mountain range worthy of a space discovery! You, my friend, probably didn't get the avalanche part, did you? You're a bit slow on the uptake, aren't you?