This one aired way back in 2013. The Macallan 25 mention is from the final episode of season 2. In the latest scene Louis (Rick Hoffman) orders himself a 25 year old Macallan. The clip itself is rather short but I couldn't let it go since I'm such a sucker for Macallan.
Louis actually gets insulted for ordering this drink. How insane is that? Pretty hard to come up with a manlier or more sophisticated drink than a (neat) Macallan 25. Ok, I'd better slow down before I run out and take the writers of Suits hostage.