my friend has his subs hooked up to a home reciever, and after a while it pops and goes silent, then it comes back on and pops every once in a while. when he turns it up, it pops and stays off. is he being an idiot and frying his amp?

Let me guess, he hasn't presented an 8/4 ohm load (whatever the receiver wants). So indeed yes, he is killing his receiver and needs to start understanding impedance loads before going any further.

Usually, no good is going to come from a setup like that...