You never forget your first.
First times are special. Everyone knows that, no matter who you have it with or when. Even the Teen Titans remember their first times (those who've had them). Although the Titans are as close to one another as any family, they've never discussed it among themselves and likely never will.
Beastboy's first time occurred in a moment of primal passion. One terrifying, ecstatic moment when the green hero let go of all his human hang-ups, neurosis, and moralizing and embraced his animal instincts. The funny thing was, Beastboy hadn't been aware of his feelings until it was all over, and by then of course it was too late to change anything. It was all over in a matter of minutes (though at the time it felt much longer), but the impact of that moment changed him radically. In truth, he's more than a little ashamed of it- he feels that he should have stayed in control.
Starfire's first time remains a cherished memory for her, one that she turns back to whenever she feels sad or helpless. It was a joyous explosion of emotion that let out years of repressed feelings. She will never forget the look on his face when she made her feelings clear- the surprise, the disbelief, and most of all, his inability to believe that she felt this way about HIM. That of all her options (and there were many, at the time) she chose to do this with him. She doesn't talk about it, but not because she feels it is shameful or embarrassing. Rather, she knows that Terrans do not think about such matters in the same way that her people do, and she doesn't want to make her friends uncomfortable.
Cyborg's first time was… debatable. It happened after a wild party in his high school days. Like everyone else he'd been drinking, and his judgment wasn't everything it should have been. He took a ride home with a girl he sort of knew from school- not friends, but more than acquaintances. One thing lead to another, and by the end of the night, the boy had become a man. Most of those who know the details insist that it doesn't count, and Cyborg will readily admit that their arguments make sense. But in his heart, he feels differently. He feels ashamed of how his judgment slipped, and how much it changed his friendships in High School.
Raven's first time was the result of a moment of weakness. She abandoned a lifetime of Azerathian self-control for just one second when she'd first come to Earth, and it happened. It was with a guy she barely knew, and would never see again. She hates herself for that weakness, hates what happened, and for the fallout of the event. She hates the way what she did challenged her view of herself. But most of all, she hates herself for having enjoyed that sensation of release, and for craving it even now.
Robin has not yet had his first time- his...unusual upbringing has prevented him from being able to do so. Indeed, he has no idea that any of his team mates have had theirs. Far from being burdened by this, the Boy Wonder is proud of having preserved his innocence. This same pride makes the other Titans uncomfortable, and prevents them from sharing their experiences with one another. The Titans don't talk about the subject much- as is understandable among a group of young people.
But they never forget their first.