When you're so horny you're throbbing, and you feel absolutely fantastic and ready to jack-off and have fun! Usually applies to partying situation where there are lots of hot guys/girls around and you can just feel yourself throbbing so hard..
Man, that girl makes me feel so throbtastic!
Mm.. I'm throbtastic tonight.. I'm going to have an awesome night.
Oh wow, I think someone's a liiiitle throbtastic there!