Stick in the mud

A stick in the mud is a spoilsport or an overly staid, conservative person and this usage dates from the mid-19th century and derives from the obvious allusion of being stuck in an environment from which it is exceedingly difficult to remove oneself. It appears, however, that the expression itself dates from about a century earlier, during the 1700s, when a stick in the mud was an outlaw or criminal but this usage and meaning has long since died away.