A person who is very uptight and unwilling to break a few rules now and then to have some fun, or unwillling to allow others to break rules, similar to a party pooper. They are also apprehensive about spending money on entertainment.
That guy next door called the cops last time I cranked up my sound system. What a tightwad.
My mom's such a tightwad, she wouldn't spend $30 on a DVD player.