I do think we need to keep a sense of proportion here.
Yes it is common sense that glassware (and all loose objects) should be stowed for landing but equally, surely the pax's own common sense would say call over a crew member and hand the glass over or drink up and stow it in a seat back or drawer, not hang onto it and start a Flyertalk talk thread.
There are much bigger issues this week than a champagne glass.