Yeah, you ought'a get pretty loaded to pull this one off. I can't imagine you really enjoying it unless you get so drunk that you end up crying against the rest room hand-dryer because you remember back in 1989 when you were at the Dallas Airport Radisson for the Ceramics In Hospital Furnishings Conference and you saw your high school chemlab partner across the lobby but you didn't wave hello because the conference was about to begin and you wanted to get a table nearest the dais. And even though at the time it was 11 years after graduation, tonight, here in the Wichita Airport Chili's rest room you're just beside yourself with disgust at what a selfish, miserably insulated person you can be.
Well it's never too late to apologize. Who cares if he/she didn't even see you that day. If a tree falls in the forest and no one is there to hear it, you're still a cock. So go back to the bar and start composing a letter on bar napkins. Under better (read: "sober") circumstances, the letter could be as simple as, "I saw you many years back and I wish I'd said hello but I was in a hurry." But if you write less than thirteen pages of the most deeply confessional prose, apparently you don't really care about this person. Start with why your son stopped speaking to you. With a nice seque, you could be deep in the muck of you not crying at your mother's funeral by page five. For the big closer, confess to sleeping with his or her boy/girlfriend the summer after graduation and then turn it all around and blame him or her for the two of you losing touch after the chemistry final. Don't worry if you forget to include the part about apologizing for anything. The point is you're clearing the air once and for all.
You could wait till tomorrow to transfer the text of the bar napkins to hotel stationery, but you have a plane to catch. Just drop those napkins in an envelope and send it on its way, tonight, before last call. He/she used to live three doors down from you in high school, remember? His/her parents probably still live there and they'll forward it. Drop it in the mail and get to bed. You're gonna sleep well tonight, friend. Because today's Write A Letter Of Apology To Someone Who'd Forgotten All About Your Very Existence Over A Decade Ago Day!