The speaker is strongly attracted to someone and wants to act on that desire instead of staying cautious. At first, she asks him to understand what she needs and to give her a chance to show her interest. As the song continues, her excitement grows: she says she is losing her composure and is ready to break rules. The mood is playful and bold, though there is also some tension because another person may be involved.
โBe badโ does not necessarily mean doing something seriously harmful. Here, it seems to mean behaving in a daring, flirtatious way and crossing boundaries she would normally respect. Saying that he makes โbadโ look or feel good suggests that his appeal makes risky choices seem tempting. โLosing all my coolโ is an informal way to say she is becoming less calm or self-controlled.
The lyrics also hint that the man may already have another girlfriend: the speaker says she does not want that girl to see them โmessing โround.โ This makes the desire more complicated, since the excitement of breaking rules may come with secrecy and possible hurt. Still, the song does not explain their relationship or say what happens next. โBadโ may be a playful pose, a genuine wish to take a risk, or both.