Ununbium is my new favorite insult. It's not actually an insult, it's the 112th element in the periodic table, but if you say it in a scornful, insulting tone of voice it works quite well. Try, "You Nunbium! I bet you didn't even know there was a 112th element!"

If you're wondering, there's 118 elements and Ununbium wasn't created until 1996 so if you didn't know it existed because you graduated from High School before, say 2000, I wouldn't actually call you a nunbium.