Thems fightin' words! Music's original mouthy bad boy Liam Gallagher is taking a bite out of Kanye West -- and his performance at the 2015 Brit Awards.

Last night Kim K's big man performed a new tune, "All Day," at the 02 Arena in London -- and the unruly Oasis singer was having NONE of it.

After the performance, which included back up performers as well as collaborators, Gallagher took to Twitter to slam the rapper, simply writing, "Kanye West. Utter Sh-t. LG x." The 42-year-old Brit also added another dig, "@kanyewest ...And you're a million miles away from ."

Take that Kanye! We wonder how the outspoken "Black Skinhead" will respond? Whatever the reaction -- Liam better arm himself because a battle's been waged!