Among the people forming the angry mob that attacks Johnny towards the end of the episode I.Q. Johnny, you can see Squint Ringo, the Amish farmer previously seen in the episode Witless, and the lady Johnny tried hitting on at the beginning of the episode Charm School Johnny.
During the restaurant scene at the end of the episode Get Stinky, sitting at the tables in the background, you can see other characters who have appeared in various episodes of Johnny Bravo. The easiest ones to spot are Melinda, the black girl introduced back in the episode Witless, who has also had cameo appearances in a lot of previous episodes, and a gray-haired version of Alfred Leechy, the professor introduced in the episode Johnny on Ice.
The restaurant Johnny and Stinky go to at the end of the episode Get Stinky is called "Chez Shi Shi".
In The Hansel and Gretel Witch Project we learn that Johnny can play the works of John Philip Sousa on his nostrils.
John Philip Sousa (November 6, 1854 – March 6, 1932) was an American composer and conductor of the late Romantic era, known particularly for American military and patriotic marches.
In The Hansel and Gretel Witch Project we learn that Johnny can play music with his nose.
Johnny: The neighbor's dog told me to steal cable!
Johnny (after the witch threatens him to turn him into pastry): Can I lick the spoon?
Scientist: Sir, how do you feel?
Johnny: Usually like this. (starts touching himself with his fingers)
At the beginning of the episode Get Stinky we see Johnny playing, pretending to be a super-hero called "Arachna-Guy". This is an obvious spoof on the famous Marvel Comics character, Spider-man.
The episode The Hansel and Gretel Witch Project is also a parody of the famous fairy-tale, Hansel and Gretel, by the Brothers Grimm.
The title of the episode Get Stinky is a spoof on the title of the popular American comedy television series Get Smart, which aired between 1965 and 1970.
The episode The Hansel and Gretel Project is a parody of the low-budget American horror film The Blair Witch Project, released in 1999.