Unlike the famous "lol" or "omg" this word has a very poor chance of being remembered as an internet acronym, so stop using it. Gaia fagggots.
Now more commonly typed as "nou", rather than "no you" or "no u".
Using this word in an argument may cause your friends to think you as simple minded/retarded/a dick.
datwunguiolol: nou (No, you)
2: Phone: Jeremy? Hey, I need you to go pick up supper for me. It's getting late and your sister is probably hungry.
Teen: nou (No, you)