You've levered a stubborn tire on the rim and are about to inflate it when you notice the tube is misaligned so the valve stem is canted over at an angle -- and grabbing and pulling on the tire doesn't seem to help.

Put the wheel back on the bike completely deflated, spin it up by hand as fast as you can in the direction the valve is pointed, then grab the brakes so the wheel stops suddenly. Repeat a few times and the valve will be aligned.