Chris Freytag Health Blender Travel Mug

I had this same problem, and after several minutes of straining/making faces that terrified my wife and kids, I broke down and reached for the manual. Having finally prevailed, I offer a two-part solution:

1. Hidden in the manual is a key fact--the lid is threaded BACKWARDS. To open the lid, one must turn CLOCKWISE.
2. Considering that I had just spent several minutes making a tight lid even tighter, a special tool was called for. I have something called a "Monster Grip" that consists of a long rubber strap attached to a sturdy plastic handle. Using that tool, carefully, so as to avoid breaking the handle, I was able to open the lid, which was still quite tight through the first half-turn.

My husband and I had the same problem until I asked him to try one more time. Instead of righty tighty it's righty loosy- like the manual says. Good Luck.