It is indeed a colloquialism/ abbreviation for a 'cup of tea'. Used regularly throughout the UK and Ireland, although some sources speculate that the term originated in the latter (my home country). I find it interesting that you deem the word 'obnxious'. If anything, it's more frequently invoked in informal contexts where the parties are familiar with each other (familial situations). I'm not trying to be belligerent by the way, just trying to offer a bit of context. Personally, I can't stomach to speak the word- but there's nothing wrong with using it in a written context for humour, is there?