The term “stupidest item ever added to TF2” is obviously one of the more subjective terms one could use to describe a thing. It’s so heavily dependent on personal experience, opinion, and bias that no item could truly just qualify without question as “the stupidest item ever added to TF2”. Which is why you may be surprised that there actually is an item that indisputably qualifies as the stupidest item ever added to TF2, and it’s not the one you’re thinking of.
It’s not something overpowered. Overpowered weapons fill a role in TF2 by letting players who equip them perform better and thus feel better about themselves. It also wasn’t stupid of Valve to add them in the first place because the stats can always be adjusted, and many overpowered items were later tweaked into items that everyone’s okay with.
It’s not something underpowered. Underpowered weapons can sometimes shine in situational… uh, situations, and many players feel a sentimental love for some certain underpowered item that just clicks with them due to either playstyle, aesthetics or some secret reason only they can understand. Mine is the Sharpened Volcano Fragment. Also, once again, Valve can always tweak the stats.
It’s not a class. TF2’s nine classes and their relative strengths can be debated to kingdom come, but each of them is so heavily entrenched in the meta, has so many different unlocks and playstyles and people who main them, has such a memorable and dominant personality in Valve’s repertoire of successful characters that TF2 would be a lesser game without every one of them.
It’s not a cosmetic. How can something that doesn’t have real stats be stupid? At worst it can make it a bit harder to distinguish someone’s hitboxes, remind certain people how much they hate candy-colored unicorns, or just flatout break the artstyle, but plenty of cosmetics do at least one of those things. Also, they are all fulfilling their function of being a costume piece that changes your appearance. Valve can’t be considered stupid for adding any one of those in particular.
It’s not a map. Every map provides a new arena for players to enjoy, and every type of player deserves to have the maximum amount of choices available to them because everyone likes different things. There’s a market for chokey hallway-filled spamfests, there’s a market for one-dimensional simpletons with lightning fast rounds, there’s a market for maps that are perfectly balanced but comp TF2 decides they need a _pro version anyway to get rid of the snow. Not to mention if you don’t like a map, you can easily go play on a different one. If you don’t, you’re stupid, but the map isn’t.
It’s not sprays, because despite appearing useless, there are actually—
It’s the Strange Haunted Kritz or Treat.
Added during Scream Fortress 2014, It was one of the many, many, many Halloween items that you could get from the stupid presents that everyone hated because somehow Valve found an even less fair method of doling them out than how they’d done it in previous years. The items had a chance of being Strange Haunted, meaning they’d track Carnival Underworld Kills and Carnival Games Won. In addition, the Kritz or Treat was a Power Up Canteen reskin, meaning that you could also deploy Upgrades on MvM! What a versatile item! Too bad it took the slot where your spellbook would normally go, meaning if you wanted to use it on the only map that incremented the strange counters you had to forgo spells. Considering the Carnival of Carnage implemented spells into the gameplay more deeply than any other map, that’s pretty crappy.
But it doesn’t stop there, because it’s also Halloween/Full Moon restricted! And unlike every other restricted cosmetic, this actually inhibits its actual job because if you try to equip it for MvM when it’s not a full moon:
It succeeds neither at being a strange weapon nor at its actual function of deploying MvM upgrades. The player is inconvenienced no matter how she tries to equip this item. It’s worse than useless; it’s actively sabotaging the player except for 16% of the calendar year assuming they never play on sd_doomsday_event. And there’s nothing Valve can do about it, because if they lifted the full moon restriction and added spellcasting ability (both necessary tweaks) it would become a straight upgrade to both classes of action item currently doing those things. Not to mention Valve stated very clearly that every community-contributed item from Scream Fortress would remain restricted forever, so they have a vested motivation to not break their word. Ultimately it’s a useless and self-defeating mess that has no hope of ever being fixed. And that’s why its the stupidest item ever added to TF2.