informal someone who complains all the time and is never happy.
Of course, your father, old misery guts, wanted to come home after half an hour because he was bored.
misery guts
noun a habitually miserable or complaining person AUSTRALIA, 1981
misery guts
An unhappy person who always complains. I don't like talking to Paul because he's such a misery guts and always squashes my good mood.
(a) ˈmisery guts
(informal) a way to describe somebody who is never happy or who complains a lot: What’s the matter with you, misery guts?He used to be good fun, but he seems to be turning into an old misery guts.