While reading an Internet article on politics, I reluctantly ventured into the comments section. Have you ever noticed that many of the commenters can’t spell?
This time, it was waist versus waste. The comment writer advised others not to waist their time.
Waist is a noun denoting the most narrow part of the torso. In Don’t waste your time, waste is a verb denoting doing something that doesn’t give you enough in return to make it worthy of doing. Don’t waist your time has no meaning.