Kirk was a walking STD.
Riker was a playboy.
Neelix's jealousy caused a toxic relationship.
Bashir was overly horny, he kept getting rejected.
Wesley had that one episode where he was up for anything, and the writers of the show changed direction for him. Except for that other episode where the 16year old Wil Wheaton kissed that 26year old actress.
Quark has to be the biggest creep. He used his holo-suites as a brothel. He had a clause in his employees contracts that made it mandatory for them to sleep with him... Not to mention he tried to scan Kira that time to make a sex hologram of her.
And he let little Jake Sisko into his establishment with all the shady shit going on... That was very bad parenting on Ben Sisko's part though.