Practice... There is a reason why I am a high-functional autistic. Why I am in a leadership role, and why I have been in one for over 4 years now... It's because I have learned how to pick up on most social cues face to face.
It's harder to do online, but it is a reason I research before commenting in most cases. Other times I just watch what other people say and then make an opinion on it based on others' reactions. I also research to verify that they are justified in their comments or they are just trolling themselves.
In other cases I can tell Monty is lying because he is blatantly being an asshat.