Where do you draw the line between what's funny and what is offensive?

So last night I watched (for the first time) Eddie Murphy’s “Delerious”. I laughed my a** off at everything he said.

Tonight I watched another comedian (didn’t pay attention to the name but he did/does roasts on “The Burn” I think). Funny as hell and way more offensive/politically incorrect.

I remember back in high school getting very pissed off and offended by a “starving ethiopian/donut” joke. I just couldn’t see how a group of starving people could ever be considered funny.

This comedian was talking about rape and sexual molestation, etc none of which I find to be the least bit funny and yet, I still laughed my butt off.

I want to feel guilty but I don’t. Just a mild curiosity for why we can be disgusted with something on one hand and find it funny as heck on the other. I know the obvious answer (context), just looking for more imput.