The kind that thinks communism is the same as nazism and thinks communism is when the government does things.
I hate liberal brain worms.
They seriously do as much damage to the left as fascists by punching to the left and spreading capitalist anti-left propaganda. They overall weaken leftism and help fascism.
We need more left unity, folks. Fash ain't gonna bash themselves. 
How do I deal with them? Poorly. If you're going to engage with one, you'd probably need your theory on point and get your persuasive pants on. You'd have to be ready to field questions like "so you're okay with political violence?" or "China is capitalist though." Sounds like they'd likely grill you on Ukraine and the 2024 election. "Putin's puppets" and "you're a Trump supporter."
The only winning line I can imagine is being well researched, concise, patient, and then finding some common ground once you field 2 or 3 accusations. You'd hit them with your philosophical justification for solidarity like "I was really moved by MLK's letter from Birmingham jail when he talked about lukewarm acceptance and decided that I agree that you should never put a timeline on someone else's freedom."
How to Save a Life starts playing
He will do one of two things, he will admit to everything or he'll say he's just not the same and you'll begin to wonder why you came.