The only time side slippers and beginners irritate me is when they are in way over their heads or when they're not considerate. When I was just getting started, I knew I needed to take up most of the run and that I couldn't maintain a lot of speed. When I got in a crowd, I'd simply get over to the side and stop and let the crowd move on, then I'd fall in behind them. I wouldn't do what most of these asshats do and continue to take up the entire run while everyone else had to weave and dodge to get by my flailing ass.
I also agree about the newbies who boast about handling blacks and tougher blues when they're simply in survival mode. If you're just side slipping a run, you're not learning. Head to an easier run so that you can actually work on developing.
But, at the same time, nearly every time I'm up, I see someone be an asshole or joke a beginner simply trying to learn on a green run or an easy blue. These are the people I'd like to punch in the fucking face. Listen asshole, every single one of us were there at some point. Encourage the beginners who are out there trying to learn and are having fun and being respectful. I make it a point to throw out some words of encouragement to at least one beginner every time I ride.