<3
So this didn't exist and I thought it did. Anyways. Assault Vest is an interesting item. When held by a Pokémon, it increases the Sp. Defense stat by 50% but requires the Pokémon to only use damaging attacks.
Competitive Use
The defensive potential of this item is quite huge. However, Assault Vest in Doubles has that huge sacrifice in the loss of Protect or Detect, so it's more suitable for Pokém capable of surviving long enough to make use of their abilities.
Potential Users
You know who's a decent user of Assault Vest? Our beloved Scrafty. Already quite bulky and uses mainly attacks, even though you lose Detect which is a huge hit. You'd need to get rid of enemy tops, too. Is the defensive potential good enough to ditch Detect and keep Scrafty as a support mon that only attacks? Fake Out, Crunch, and Drain Punch are quite useful, allowing for a new moveslot to use Ice Punch, Rock Slide, Stone Edge, Smack Down, or Zen Headbutt.
Togekiss. He already has a nice typing, with decent defenses and a nice movepool overall, this small annoying support Pokémon could put Assault Vest to good use, especially with that goddamn flinching Air Slash.