There's just something special about having a glass of wine next to a dinosaur. With its cavernous main room and sprawling exhibit space, the ROM is a perfect location for a multi-faceted party. DJs and a long bar on the main level, more DJs or live bands in each room of the second floor, and food stations peppered throughout. It's easy and enjoyable to keep moving all night with different experiences in each area.
The crowd is pretty mixed - groups of students, 30-somethings, and a few middle-aged couples and friends. Some are there to drink/chat with friends, others to party/dance, and some just to explore the museum exhibits for $14/person. For the latter group, there are a few areas where drinks are not allowed so you can escape the party scene.
I highly advise purchasing tickets in advance (i.e. at least a few days before). They leave a large portion of tickets to be sold at the door and there are always massive lineups. The event is only from 7pm - 11pm so it's a shame to miss so much of it waiting in line.
I've been to three events with themes of dinosaurs, fashion, and Halloween. I look forward to seeing you at another one soon!