stick-in-the-mud
Idioms, phrasal verbs and collocationsmeaning: a dull, boring or uncooperative person
If you put a stick in the mud it's very difficult to move that stick. It will probably just stay there doing nothing.
examples: Robert is no fun, he's a stick-in-the-mud.
Dan never changes his habits. That old stick-in-the-mud is in bed by 8 pm every night!