Magnatize simply means Hooking up, or "having sex" in old school terms. Magnatize is a clever term most often used in the club scene as a way for a man to inform his current dance partner he would like to proceed in inserting his cock into at least one of her sex holes sometime that night.
(Random Techno music in the background)
Man: "Hey baby, you wanna magnatize"
Blonde: "Wow, you're classy. Of course I want your meat plowing me, but only if you promise to empty your balls in my mouth.