Why do some people think tomboys are lesbians?

In every culture their are behavior expectations based on gender. For instance, in Scotland it is very normal for a man to wear a kilt. In the United States, if a man chose to wear a kilt (basically a plaid skirt), he would be considered extremely odd by people who are ignorant of Scottish fashion.

These expectations based on gender are called "gender norms". When someone behaves in a way outside the normal behavior, the social group responds negatively to those people. Sociologists believe that people began enforcing conformity because culture creates a group identity that helps cement groups of people together so that they can be more effective at survival.

There are two reasons why the negative response in the United States is call someone behaving outside the gender norms homosexual:

1. The issue at hand is sexual identity, and to young people who are not yet sexual the "norms" are what they relate to the term sexuality; and

2. Homosexuality is deemed a negative trait in United States culture. In cultures that consider it as normal a sexuality as heterosexuality, this term is not used to insult people because they would find no insult in it. Imagine if someone attempted to insult you by calling you "Blue Eyes" or "Left Handed". In our culture we would think they are ridiculous because neither having blue eyes or being left-handed are negative traits.