* In the earliest books, Chet Morton was often portrayed as an irrepressible prankster, and often the books would have a chapter concerning one of his pranks as filler material or to help the plot (IE: in "Tower Treasure", to prevent the bumbling police detective Oscar Smuff from ruining Fenton Hardy's interrogation of a dying criminal, [[FunnyAneurysmMoment Chet comes up with an idea to make a fake "bomb" by putting an alarm clock in a box and hiding it under a fruit stand, and has another boy find it under there. The proprietor alerts Chief Collig and Detective Smuff, causing a major fuss and thus making the policemen miss their train]]). Sometimes it could come off as being a bit douchey.
* After being set up with fake credit cards planted in their van and interrogated by Chief Collig, he dismisses them easily, but in a gruff manner. And then Joe asks:
-->''Are we still friends?''
* The always-stoic Gray Man once treated the boys to a meal, and he complains that they almost ran his paycheck dry with the bill.
* Bowling as ''Aunt Gertrude's'' hobby is funny in of itself already, but the fact that she does it to ''relieve stress'' makes it even more hilarious.
* At the end of ''Acting Up'', a Bollywood star they befriended decided to have a little fun and directed a few of his fans to ask Frank for an autograph, introducing the latter as a foreign star. Joe couldn't keep a straight face and wanted to kid Frank about it, but Frank got the last laugh when he told Joe he signed the autographs in ''Joe's'' name.