Tight Assed 

When everyone keeps good/fun things to do on the down low, such as a good house party.

Theres never anything to do cause everyone around here is so tight assed all the time

Tight Assed by pctvguy March 16, 2008

tight-assed 

be tight-arsed or tight-assed(British & Australian, very informal, American, very informal)

to be worried about small details that are not important.

Cambridge International Dictionary of Idioms © Cambridge University Press 1998

Don't ask Jack to get involved, he's so tight-assed and really irritating.

tight-assed by dulcederonda January 30, 2008