The above answer, “Sorry, my rav says it’s an issue” is surely the best reply. You don’t even have to ask him.
First names: Rav Falk (Manchester) says it’s assur. Also, Rav Chiam Pincha Scheinberg ztal, said it’s assur. When asked, “But what if you’re close friends?” , he answered, “Then you’re too close!”
If there’s no last name, say “rebitzen”.