It's a combo commuter cup and vacuum bottle (Thermos).   I thought it would be neat if the little cap on a big insulated bottle was larger, and was useful on its own.  The solution: take the lid off a commuter mug, and screw the mug down in place of the cap of a bigger bottle.  I  bet some of them out there would actually fit unmodified.

Now I just wish they made them with glass on the inside instead of plastic.