They can be a bit tricky to shift, though personally I've not been defeated yet. I guess it depends how much practice your wrists get. You can get multipurpose grips from Amazon and the like for old dears, which can lever them off. But the one thing that does seem to work is to put some plastic foil from say a sweet wrapper, wrap it around the cap and use that as a barrier between your hand and the cap as you twist it. There is another thing that I hesitate to suggest since I fear for the consequences: starting with your table in the upright position against the seat in front, wedge the cap between the table edge and the fabric on the seat in front. Press one hand on the table to keep it firmly wedged, use the other hand to twist the drink. You can of course request the person in front to recline their seat, to assist in this process, and once you have resolved the cap issue you can invite them to sit back upright again.