People can be kind of jerky. My suggestion is to smile in the face of their annoyance. Don't let their annoyance ruin your ride ... that kind of attitude is a reflection of them, not a reflection of you or your riding ability. And if they're on an "easy" trail, they should be expecting to come across beginner riders, and should be in the frame of mind to deal with that.

However, that being said, I have ridden with a lot of beginner riders who seem to be unaware that they're blocking riders coming up behind them. When it's safe, and only when it's safe, get out of the line as quickly as possibly. It's a total bummer to have to come to a complete stop in the middle of a section of trail that requires some momentum, because the beginner in front of you is stopped or walking their bike right down the middle of the trail.