Get rid of the idea that people are always watching you, sizing you up and evaluating you. The only people that do this are shy people who spend a lot of time fearing that they are being evaluated negatively. The reason you think you are being watched is because you do this to others.

The solution to breaking this habit is to stop judging and sizing people up and you will stop thinking that others are doing the same to you. Don't worry about people evaluating you unfavorably because the reason for this is that they think they are better than you.