When one is considered more than just ordinarily sexy;
to be used similarly to when one describes a person as "hawt", instead of just "hot".
Pronounced sex- -see. Spoken with a pause between sex and see.
Someone who knows too much about sex. So deep about sex. A mind sex perv. But doesn't act porn or isn't a fuckboy. Normally the knowledge is gained from watching too much porn and reading or watching lots of erotic stuff.
Alice: Damn Luke, you such a fuckboy.
Luke: You're wrong, I'm just a sexcylopedian.