tang, n.² — Green’s Dictionary of Slang

tang n.²

[SE tang, a flavour; such a person gives the situation an ‘unpleasant flavour’]

(US campus) someone who puts a damper on things.

1973		Eble Campus Sl. Mar. 4: tang – a person who brings you down, a bummer.
1996		Eble Sl. and Sociability 59: Derogatory epithets abound, for example [...] tang, three dollar bill, tool, twerp, twink.