Drinks before event-Yonge and College?
The bar at the Pantages Hotel is open from 4pm onwards. It would be a 5-10 minute walk from Yonge & College.
Not sure what time you need to meet him, but they have a piano bar on Fridays nights and djs other nights of the week. I'm sure they would have coffee and other non-alchoholic drinks if you requested them.
The Senator Diner on Victoria might be another option. Not fancy, but a nice atmosphere, and they've got a lot of nonalcoholic drinks like milkshakes and cherry cokes in addition to coffee.
The Consort Bar at the King Eddy on King E is one of the nicest places to meet, if you like a classic atmosphere, but it would be a 15-20 minute walk from College. Another option might be 8 wine bar at the Cosmopolitan Hotel, but that's on Colborne Street south of King, so it would also be closer to a 15-20 minute walk.
where's the event? at the Carlu, maybe?
If you're all dressed up, I'd imagine you won't want to walk more than a block or two.
If you want to go somewhere nice, you could go to Avenue at the Four Seasons, or the rooftop bar at the Hyatt at Avenue and Bloor and then hop in a taxi to the event.
If you're wearing a big formal ball gown, I don't know that you'll find a venue with others similarly dressed, regardless of where you go...
I can't think of anything nice at Yonge and College.