Instead of trying to yank it off; put your thumb between the rim and pump near the stem and, while steadying the pump with the other hand, slowly pry it off the stem. That makes the pump come off straight instead of sideways like a bottle top opener. Or, grip the pump like using a cork screw to open a bottle of wine and pull off. In either case, straight off instead of levering the pump.
Without seeing the tube or pump but knowing how these things happen I vote C: poor technique.
Last edited by Happy Feet; 06-03-18 at 03:24 PM.