Are you folks familiar with the surfing 'minigame'? It came about on Counter Strike but has been on TF2 for a while now. It's not as popular anymore but there are still some servers around that are great for practicing on.
It's basically strafing against a slanted wall to make yourself slide across it gaining speed, going through obstacles and several jumps.
They're fun to just chill on after a good couple rounds of vanilla or MVM. Some servers compete for having the fastest time on a couple maps. The air strafing is also helpful for when you're being juggled by a soldier in regular play, although it's not as dramatic. I know a couple ips if you guys are interested
Here's the TF2 wiki page for it as well.