We used to get a similar sort of chap at my old local's karaoke nights. Took it very seriously, told us he just did this on the side when he wasn't gigging, but was very well known and used to be successful. His singing was passable, very over-the-top pub singer type - but he was clearly delusional. I think there's just one for every pub isn't there really.
Side-note - he tried to buy something I was selling on FB Marketplace recently and I remembered the name. Tried to get him to pay up front because he wanted me to deliver it, and I still very clearly remember the message he sent... 'I WILL NOT LET YOU DOWN'. Very sinister.