I know someone who hates pictures of herself, never took a selfie in her life, but switched to a picture of herself and used her real name simply because it's less likely she'll say something stupid/inflammatory in the middle of an argument. If you're using some random name like chickenslippers1981 and have a pic of a cat, you might feel less like being thoughtful. You can always walk away from chickenslippers1981/cat, but you can't walk away from yourself.

This is probably a pretty decent heuristic actually! My guess, as an armchair psychologist, is that narcissism and a toxic need to generate attention and drama are highly correlated with constantly taking selfies and sharing them. Look for the profile picture and just a quick glance at the feed, and if it's full of selfies, you probably have a pretty good idea of who you're dealing with.