This only really happens to me in 4 mans. I'll politely ask someone not to do it if it seems intentionally, for example if someone regens me before I pull but after the last pack is dead. I try to be very polite about it.

"If you don't mind can you please not regen me before the pull, it makes you a hate magnet."

It's about a 50/50 chance that i'll get a healer that just says "ok, sorry" or the fun one "DON'T TELL ME HOW TO PLAY MY JOB!".

If its the later then i'll generally just ignore him and click it off before pulls. Just a fact of life in the world of FFXIV.