Originally take from James Hetfield's guitar on the Metallica black album tour which said "EET FUK" it was then turned into 33T as influenced by 0wn3d to use numbers instead. This term is used similarly to 0wn3d, more so to taunt others when something good happens for you and something bad for them. Similar to the phrase "Eat it!" as well.
"33T!" , "You just got 0wn3d, 33T!"