Noun: A notorious and persistant moaner. An incurable pessimist. A Mannington is not bad company per se, but can be a pain if stuck with on a slow train or in a lift (suicidal tendencies are highly contagious!).
Stu: Top of the morning!
Mannington: Awww, for fuck's sake!
"I tried to persuade Luke to go to the pub with us, but he did a Mannington and just ranted about his workload."
"Come on, cheer up mate! Don't be a Mannington."