A great Wikipedia nugget just discovered:

It was also at this Council [of Constance, 1415-19] that a cardinal ventured to correct [Emperor] Sigismund’s Latin (he had construed the word schisma as feminine rather than neuter). To this Sigismund replied: “I am king of the Romans and above grammar.”

This is almost as good as another quip, from Ferdinand I of Austria (r. 1835-1848), who is:

best remembered for his one coherent command, to his cook when told he could not have apricot dumplings (Marillenknödel) because apricots were out of season. He said “I am the Emperor, and I want dumplings!”