Wiktionary
stick in the mud
alt. 1 (context idiomatic pejorative English) A person unwilling to participate in activities; a curmudgeon or party pooper. 2 (context idiomatic pejorative English) More generally, one who is slow, old-fashioned, or unprogressive; an old fogey. n. 1 (context idiomatic pejorative English) A person unwilling to participate in activities; a curmudgeon or party pooper. 2 (context idiomatic pejorative English) More generally, one who is slow, old-fashioned, or unprogressive; an old fogey.
Usage examples of "stick in the mud".
If only you weren't such an old stick in the mud, she thought, then tried to pretend it wasn't a thought she'd had at all, since it was so ungracious.