actually there have been 3 other episodes with River Song where she quotes the rules to the Doctor
If “Bowties are cool” is a rule, it seems to me “Fezzes are cool” should be one too, although River Song and Amy would clearly disagree. (Also, did he say that about cowboy hats too? I can’t remember.)
I wear a Stetson now. Stetsons are cool. 
“I wear a stetson now. Stetsons are cool” - The Impossible Astronaut
River didn’t like the stetson much either…
But there isn’t a #54 in that link. Were you lying?
Pardon the mini-rant, but you know that scene, later in the episode, where the Doctor is unconcerned about being surrounded by armed Secret Service agents, until River reminds him, “They’re Americans!” It’s a good line, and I don’t mind a little ribbing over America’s gun culture, but it bugged me that it was River saying that. This is a woman who, not fifteen minutes earlier,* fired a loaded hand gun at her husband’s head because she thought it was funny, and she’s going to criticize someone else for being trigger happy? Bitch, please.
*Or forty year later, depending on how you count.