At first, this doesn't seem like a big deal. It's just your typical USB flash drive. Batman probably has hundreds of these laying around so he can give intel to police and other superheroes in a secure fashion. They all know it's from Batman because it's got the bat-symbol on it -- and that's the most baffling part.
Batman's ego is so big, his need for himself to become a symbol is so great that he puts a bat shape on everything he touches. His whole life is like Gotham's version of "Put a Bird on It!" You can just imagine him toiling away in his Batcave during the day, scribbling bat symbols on flash drives with a Sharpie just so he can look cool when he hands them to people. Where does it stop? Does he use bat Emojis at the end of all of his text messages? Does he draw bats on his lunch in the Justice League refrigerator? Does the bat symbol even adorn his batpoon?
It's okay, you can have a second. Get it all out. Yes, Batman's mini-harpoon gun is called a batpoon. Yes, it's a term that favors word economy at the expense of sounding like the most popular room at the DC Comics brothel. Yes, according to the second panel above, Batman was generous enough to give Robin some batpoon on the occasion of his birthday. Grow up, guys. It was a different time. It's not a big deal.
Really, it's not hilarious at all. Saying "batpoon" out loud right now -- sitting in front of your computer or while looking at your phone on the bus with a dozen strangers in earshot -- won't do anything. It's definitely not the most fun you'll have all day.