Non-G

Non-G is used to describe someone as a part pooper or someone who ruins the mood. It comes from My G which can be used as my guy or gangsta.

Guy 1: Don't go to the party tonight. We can go to the library and look back at our test results and see what we did wrong.
Joy: We studied so hard for that now we want to relax! Ugh you've always been such a Non-G.