They have a reputation for undermining "the good" in some sort of pursuit of "the perfect." Too much ideology and not enough practicality. Similar to anarchists in that vein. Just mostly end up being obnoxious, overly critical of communist/socialist organizations (beyond reasonable and valid). Like they'll agree on 98/100 points and then not vote or push for whatever just because of two non-critical points. This is all abstract, but that's the idea. Contrarians, etc. Also, I personally find the term (used pejoratively) pointless, annoying, counterproductive ... similar to libs calling socialists "tankies." It's just meant to annoy people without meaning a lot. That's how I view it anyway.