‘Whatcha doin’? You must be flirting.. Flirt with me instead. It’s free.’
There must be a limit to ‘friendly jests’. There must be a limit to jokes that can be said without ‘malice’. THAT is apparently beyond the limit.
It’s not cool to joke around with that. It’s not cool. From a boyfriend’s point of view, it’s appalling. My girlfriend is not cheap. But that ‘joke’ is very demeaning. The assumption that she must be flirting is unflattering. Second, that you invite her to flirt with you (for free!) is distasteful.
I love and value my girlfriend. And whoever dares to ‘joke’ like that to her will answer to me.