This lady in my building asked me to help her with a heavy box. Do you think it's okay for me to tell her I don't want to help?
Why don't you want to help her?
I'm a guy and I think it's sexist that I'm expected to lift things for people.
It's annoying to be expected to lift heavy things for people, but you should try to help where you can. Just as tall people are often asked to reach things, stronger people are asked to lift heavy things in order to help others. If you don't use your strength to help others, then people will assume you're rude.
But, sometimes I really don't feel like helping, I'm not a slave!
Of course, no one should force you to help, but it's probably pretty easy for you to lift the box and she might not be able to lift it at all. Sometimes, we have to help out others even when we don't want to. I'm sure you've received help before and know how thankful you were to get it.