This technique works pretty much flawlessly when mastered. An expert can even hide a boner without a shirt by using boxers to catch the boner. Trick is to have the underwear go lower than your pants and wear the pants at a good height to cover the vertical boner. You still won't be able to hide the bulge created, but that is awesome to have.
WARNING: Raging public boners still go slightly outward and may still be visible if the force of the restraint is not strong enough to keep the boner back.
Jon: "You kidding me? Of course I had a boner, but I effectively sideswiped it away like magic."
Jesse: "You are a fucking boss."
Hey Harry, I sooo side swiped Shelly this morning after our long night of rough sex and drinking at the Irish Pub!!!