An act of flatulence which occurs whilst running long distances; thereby leaving a several mile long pungent smoke trail in your wake.
Dave: What is that smell?
Jamin: It must be Matt, skywriting
Dave: That is foul! Maybe that is how he is so good, because he poisons all the otherrunners behind him!
When someone’s true feelings or intentions are extremely obvious, regardless of their attempts to disguise them. It's as easy for everyone to see as if they were writing it in the sky.
"He wants to act like he doesn't like her, but he's skywriting."