This yearbook goodbye message can be used for general acquaintances.
Dear {Recipient},
One time in {Class} you {stalled the class for an hour talking about unicorns/ran into a wall/wrecked the curve for the rest of us} and let's face it. In 20 years, I'm not going to remember that you were a wicked smart bookworm who totally killed me every year performing improv. No, I will recall that single ridiculous, embarrassing fact and announce it to the rest of the class.
I look forward to that day. In the meantime, get started on creating some hilarious memories about {their next career move} that you can tell me at the next high school reunion.
Stay classy.
- {Sender}