A male, although not necessarily young, who is aware of and enjoys his attractive qualities and grooms himself to maintain such while paying close attention to face, physical health/fitness and apparel.
Most "pretty boys" possess a high level of self-confidence which borderlines cockiness and arrogance as well as a high sense of self-awareness most consider to be vanity.
While they tend to enjoy making people smile, spending time in front of the mirror and complimenting themselves, most do not like to be called "pretty boy" but, instead, well-groomed or well-maintenanced because the term, used as slang, has also been referenced to homosexuality:
pretty = nice looking (female)
boy = young man
pretty + boy = a boy whose looks resemble that of a female (perhaps in a pink polka-dotted dress)
Preferred terms: Well-groomed, handsome, handsome man, handsome male, well-maintained, well-maintenanced guy
LL Cool J is a pretty boy because he cares about his outer appearance, from head to toe and spends plenty of time in the mirror making sure his face and body look good.
He enjoys smiling, making other people smile and he licks his lips so much it looks like he's doing a commercial for Carmex.