What to wear: Unlike Red Priestesses, the garb Red Priests wear is a little less on the nose. Instead of a red dress, suit up in some dark pants and boots, paired with a black, long-sleeved shirt or leather jacket under some red-tinted chainmail. Add in a flaming sword to complete the costume.
How to act: Make your faith in R'hllor, the Lord of Light, known to literally everyone you pass on the street as annoyingly as possible.