I love uhltimate's OTF Fidget Knife concept but thought the blade looked a bit boring, so I fiddled with it (guided version) to add a sharper-looking knife tip. Pictured here with LucasAlexander's excellent Ergonomic slider remix, which I highly recommend for ease of fidgeting: https://makerworld.com/en/models/473585#profileId-383724

I recommend 100% infill and printed in PETG to maximize sturdiness. Do be careful however: even though it's a toy it can still be dangerous given its shape!