The Thirder
A boy/girl who is a third wheel, but is the best because he/she made the relationship successful and happy. But, annoying and funny.
Jiro: Bro, James got our first kiss in 4k.
Jena: I know his annoying but he probably made our relationship official, so he's the thirder
Jena: I know his annoying but he probably made our relationship official, so he's the thirder