1) a great success (stemming from the Spanish word for success, éxito)
2) Sexy, sexually appealing
For something to be "sexito", it does not necessarily have to be "sexy" according to the dictionary of sexy. It can just be something cool, awesome, epic, etc.
It is often used as a one-word response to something/someone/an action believed to fall under the category of "séxito"...kind of like "amen."
Abigail: How is my outfit?
Teresa: So who is coming out to the bars tonight?
Abby: Me, you, Lyzzie, Matt, Tara, Michelle, Radhika, Jakim, and that guy I met last week.
Kay: Heyy, let me know when you get home safe.
text message sent 20 minutes later
Kay: u home yet