Regen is not such a big deal that you should feel the need to apologize over, or stress over too much. It isn't that bad, and aggro can be picked up. I'm not gonna go out of my way to berate a healer over it. I don't think I've even mentioned regen to healers in-game. I'll click it off, and keep on pulling. Most of the time I probably don't even bother clicking it off, or rather don't notice, so used to it. Certain pulls it can be really annoying though, like when the healer pulls off of you and runs in the opposite direction or something. It's more of a habit I got myself into more than anything else because of the times I've had an annoying experience, to click it off.