Jaco is the definition for a male that has a high body count , has multiple girlfriends , has cheated on girls before , plays girls , breaks girls heart on purpose and for no reason , purposely hurts girls mentally or physically and just completely a male whore.
Basically the male version for bop , whore , slut , strumpet etc
Girl 1: Omg Liam is just asked me out!
Girl 2: DONTSAYYES HE IS A JACO