BA do not have to offer Arabic coffee. There would be nothing wrong with them not offering it even on routes to/from Arab countries. However, if they do, then you would expect them to do it properly. Incidentally, I would expect the same in a "high end establishment" in London too: I would not expect them all establishments to provide Arabic coffee. I would expect those that choose to do it, however, to know what they are doing.

What the OP described feels rather amateurish and, well, a bit cringe-making, to be honest. You expect a modicum of refinement and discernment in F. This does not mean that banter with passengers is not appropriate but you need to feel your way first and know when to and when not to. Admittedly, this can be a bit difficult when you are young and have limited experience (although some are naturals at it), hence why many airlines consider that it is a good idea to leave F service to more experienced members of crew.