why do guys think girls can't do anything?

Hi Morgan! 
Thank you for your question. I promise that you will find men, both in the workforce and/or at school, that will believe that women are just as capable as men. Now, if you are finding yourself in a position where there are specific men that do not believe this, you need to stay clear of them. I believe co-workers should never have issues, if they stay professional and hardworking. Luckily, I have seen a drastic influential change in the workforce behavior and company policies (revolving around gender equality). I believe that men will get more and more comfortable with women being in a this type of work environment, because more women are applying and getting recognized/awarded for their achievements in this field. Hang in there - you have a lot of supporters (both men and women)!
Take care,
Allison