stick in the mud
Someone who is considered boring, often due to unpopular or outdated beliefs. Sally was tired of being called a stick in the mud by her friends just because she refused to drink alcohol. Just because I don't like roller coasters doesn't mean I'm a stick in a mud—I like lots of other fun things!
stick in the mud
n. a dull and old-fashioned person. Don’t be such an old stick in the mud.
stick in the mud, old
A person who avoids anything new; an old fogy, not necessarily old in years. This expression, which presumably likens such an individual to a vehicle whose wheels are stuck in mud, has been around since about 1700. Thomas Haliburton used it in one of his Sam Slick tales (1843): “‘Well,’ said old Stick-in-the-mud, ‘what are you arter?’”