Green’s Dictionary of Slang

(UK black) a self-referential description, emphasising one's importance, power, etc.

2017		theculturetrip.com ‘Guide to London Slang 10 Jan. 🌐 Manz – refers to oneself in a ‘big up’ manner.
2017		hubpages.com ‘Roadman Slang 4 Jun. 🌐 Man - me. [...] a lot of London slang revolves around this strange idea of referring to yourself, whether you're male or female, as ‘man’, and then conjugating any following verbs in third person. e.g. ‘man don't care’, ‘man's coming tonight!’.