Cosmo and Wanda went to the same high school together.
Apparently a lot of the students from Cosmo and Wanda's high school had lied about something personal and that they've been hiding the truth up until now. (For example, Luthor Lex claimed to the school he still does football but he reveals at the end that he now does ballet)
Timmy claims in this episode that his family have bladders of steel.
Truth or Cosmoquences - The episode's title is a spoof of the famous slang "Truth or Consequences".
Harry Potter - The owl that brings a letter wears a red-and-yellow scarf resembles Gryffindor scarf. Also, the owl could be a reference to Hedwig, Harry Potter' owl.
Lex Luthor - Luthor Lex's name is a spoof on Superman' enemy.
Timmy having to hold it despite needing to go to the bathroom.
Britney Britney saying random things.
It is said that there are no doors in Fairy World, yet doors have been seen and used by fairies all the time in episodes before and after this one. (ex. the doors at the Pointy Crown in This Is Your Wish)
Juandissimo was unaware that Cosmo and Wanda were married in this episode. However, since Timmy had already met Juandissimo, so he should have known this. He should have also known that he is not rich or famous. It is possible that he was just going with the trick to get to Wanda.