While I’m not part of this demographic, I can appreciate the design. This funnel by plastic organizer manufacturer Wowhouse is designed for protein-powder-mixing gym rats who make their shakes on-the-go, and don’t want to spill powder all over the place. And it’s available in different configurations.
I would probably try to DIY one by cutting the top off of a two-liter bottle, but I’d eventually admit that the threaded cap makes the Wowhouse offering better.