No helmet while on motorcycle
Use the following trick to ride a motorcycle without Niko wearing a helmet. Tap TRIANGLE at any point during the animation where he puts the helmet on, but just before the helmet actually appears. Doing this cancels the animation and Niko will not be wearing his helmet. If you wait too long and press that button after the helmet has appeared in Niko's hand, it will still cancel the animation but the helmet will immediately appear on Niko's head.