The ending of the episode with Grampa crashing the wedding is a spoof of the 1967 movie, The Graduate.
Grandpa performs the classical "roll dance" from Charlie Chaplin's The Gold Rush. He's even almost had been arrested for "copying" Charlie Chaplin.
The chalkboard gag is a reference to a copyright notice by Major League Baseball, warning everyone that it is copyright infringement to rebroadcast, retransmit or reproduce MLB programming without permission from MLB.
Mr. Burns usually almost cannot move, but he is able to dance swing in this episode. This isn't an error, he's weak at times, but other then that his body is in good shape.
Despite the claims of the Blue-haired Lawyer, Grandpa's immitation of Charlie Chaplin isn't violating any copyright law, as The Gold Rush has been in public domain since 1953. The Blue-Haired Lawyer is very nitpicking with immitations and retellings.
Grampa shouldn't get gas bills, since he lives in a Retirement Home.