Wiktionary
tightass
n. 1 (context slang mildly vulgar English) Someone who does not know how to have fun, or who is so worried about insignificant things as to ruin any fun that anyone around them may be having. 2 (context slang mildly vulgar English) Someone who is stingy, or who is tight with money.
Usage examples of "tightass".
Walk into the Fourteenth Street precinct after midnight dressed like a legal tightass and see where it gets you.
It's against the mandate, and you know how righteous those tightasses are about that.