With friends, we'll usually just diffuse the situation with a combination of honesty + terrible jokes: ex. "Man, I wish I could do colors half as good as you....can I eat your liver to gain your abilities?"
As for people I wouldn't feel comfortable making bad cannibalism jokes with, someone's only told me they were envious of my comic's sub count once, and it actually made me really happy. (Felt like I had finally made it to the other side of fame, ya know?)
But yeah, I offered to give them advice/crit on their work, and it seemed to all go okay.