Gavin DeGraw -- Sinead O'Connor Can Tell Fans to F**k Themselves ... I'm a 1st Amendment Guy

Gavin DeGraw thinks everyone -- including Sinead O'Connor -- has a right to tell anyone to go f**k themselves ... because this is America dammit!

We ask Gavin about the crap Sinead is both taking and dishing out after she cancelled a few concerts and fans went on an Internet tirade against her. She blasted back in kind.