Noun used to describe someone who will not participate in fun times, or someone who tries to derail a sweet prank or adventure. (See wet blanket
Adjective used to describe something that is not fun, but could have been.
"This lameass is trying to stop us from throwing the old TV off the balcony at the climbing gym."
"What is with the mimes? This is the most lameass party I have ever been to."