What really turns a guy on, is surprisingly individualistic. It varies greatly from guy to guy, but in general I'd say breasts, aphrodisiacs (link below), new lingerie, etc...
*Addition*
Some common factors can be:
For straight guys; Breasts, revealing outfits (on women), uniforms (nurse, police, etc.), large behinds
For gay guys; Crotch bulges, shirtless guys, muscles, leather/authority outfits, and a great fashion sense.
Of course as the original answer noted, it varies greatly from guy to guy.
Source: Gay male in the middle of nowhere.
The Boy Turns Man was created in 1972.
The duration of The Boy Turns Man is 1.83 hours.
When a boy turns into a girl they have their junk cut off or a girl turns into a boy and gets junk of their own
The Blue Fairy does.
Could be embarrassment.
You sleeping with a girl/boy and it turns out they were your brother/sister
Bar Mitzvah.
Alex Pettyfer
He turns 8. Nothing in Jewish tradition happens when a boy turns eight years old, however when a Jewish is eight days old, he goes through a ritual circumcision called Brit milah.
Hippo turns into a boy for the first time in episode 25.
The Thirteenth Year
Anything sexual really