It's absolutely impossible to go for a drink at Ronnie's and not bump into someone you know (or think you know, ahem, members of Broken Social Scene) either inside Ronnie's or stumbling down Nassau Street if you're on the patio.
A few years ago they had "Cosby Mondays" (show up wearing a Cosby sweater or else one will be provided for you!), where they'd play episodes of House Of Cosbys and The Cosby Show and serve Jell-o shooters but I think those days have passed and it's no longer a regular thing.
In the summer it's especially busy, with hardly a spare seat on the popular patio, but if there is one, feel free to grab a seat because everyone's friendly and socializing/intermingling is encouraged.