I haven't made many gear related custom moves but here is one:
explosive vest (intimate 4-harm area refill)
Sometimes people don't take you seriously. So you strap explosives to your body, walk up to them, and make some demands. Other times you don't intend to walk away. At least you won't be around to worry about the consequences.
Here's a custom move (untested) for the explosive vest:
When an NPC triggers their explosive vest and you have some forewarning, roll acting under fire to escape the blast. On a 10+ you get out fine, cinematic explosion in the background. On a 7-9, you get out but you lose something, choose either someone you cared about who dies in your place or suffer 2-harm. On a miss take 4-harm and the MC will get back to you when you regain consciousness.
When you choose to trigger your explosive vest, roll+hard. On a hit, choose someone (not a PC). They die with you. On 10+ choose a second person if you want. On a miss...well you are dead already.
In play the vest was never triggered so I'm unsure how well these moves would work.