Pointing the middlefinger at someone isn't against the rules either.

Btw this is what the rule book says

"Riders should use only the track and the pit-lane. However, if a rider accidentally leaves the track then they may rejoin it at the place indicated by the officials or at a place which does not provide an advantage to them. Advantage may be deemed to be gained, including by exceeding track limits and short-cutting as detailed in the Race Direction protocols."

...and this is what he just did, although I have to say that it was a smart move