The rule and ettiquitte on asking to see mucked cards at showdown?

[paveplanet]

Speaking of 70 year old grandmothers...I'm playing 4-8 limit at the Orleans waiting for the tournament to start.
Running over the game and 3 times the same old duffer asks to see my cards. I tell the dealer if she's gonna keep showing I want to see his cards everytime.
When I go to cash out +300 I tell all the grey hairs at the table "see ya next week, bring another social security check".
When in doubt sail your cards into the muck, then the dealer can't dig them out.