Imho, κομψευόμενος is equally odd nowadays as beau & dandy (which has entered Greek as δανδής).
Of the slang.gr terms, I would say that φλούφλης, λούλης, λαλάκης and, most of all, φλώρος are almost synonymous, with φλώρος being an evergreen, φλούφλης the most modern and λούλης / λαλάκης on...