I click off regen if a healer does it.
And I'll just passively continue to do so if they continue to apply it at inopportune times. Now and then you'll actually find a healer inquisitive enough to ask about it. They're the ones that get told what's up because they're willing to ask and learn. Those that don't ask will simply have a tank without regen on them, and it's not like that's a very big deal.

Of course I let regen continue if it's at an appropriate time of the pull.