Question Author
Thanks for your further suggestions Aurion and TT. I already have Idle as the answer to the clue "Inactive".
However, the Ribble suggestion set me thinking (and surfing) and I've found a River Rib (in Hertfordshire). That seems to fit nicely with "Make fun of".
That would then leave Tees for "Trifles with". However, pedant that I am, I would prefer the clue to be "Trifle with" (without the final letter "s") as it would then be grammatically correct - as indeed are all the other answers I have.
Thanks again for your suggestions.