I try to recline slowly too, but sometimes the seat gets "stuck" so I have to keep pushing harder just to get the seat to recline. And when it finally goes, I sometimes accidentally slam it back.

This is a good point. IMO I think it's OK if you are reclined during the meal service if you are actually sitting reclined. But most of the time, people leave their seats reclined even though they're sitting upright in their seat, so there's absolutely no need to leave it that way.

I actually see people reclined during boarding / at the gate quite frequently. It might be polite to wait until people in the row behind you are seated (especially in Y), but I don't think it's such a big deal.