Malignant meaning programs that aren't supportive of struggling residents, frequently violate duty hours and tell you to lie about recording it, blame you for shortcomings of the program, frequently drop people for reasons that are not justified, don't give residents leeway with regards to family issues (new birth, death, illness, etc.), basically programs that create a toxic environment for their residents. Its honestly hard to tease this out, but some ways are to just talk to residents about their programs. Everyone has things they hate about residency, but the program and especially the PD should be someone that has your back.
All that stuff about Carib grads is not at all what I'm talking about, nor do I even know what that poster's talking about. Sounds like they're speaking from some previous back experience. I've interacted with plenty of Carib grads, and I know many from before med school. The ones that make it are just like everyone else. They may on average have a higher threshold for crap just given what they had to deal with on the islands, but I have not experienced a "box of snake" attitude from them. If anything, I've seen more AMG gunners than anything else.