Do you always disregard someone's opinions based on the fact that the person is a weirdo? :-)
If you have limited time span on this Earth, sounds like a prudent default strategy to avoid wasting time with BS - at the cost of a few false negatives...
A flaming egomaniacal narcissist? Usually, yes, I disregard them. Maybe this is a flaw in me, but I don't have the patience to sift through that particular flavor of garbage to try to see if there are any gems in there.