Lick the Hanging Glider.
Mile High Club is a Steam achievement.
The easiest way to reach the hanging glider is to climb to end of the Crane arm and wait for it. When it appears, activate Slow Motion and then jump on it. You can then lick it whenever you like.
Alternatively, use the Builder Goat mutator to build a bridge from the crane out to where it flies by, and wait for it there.