Homophobia and transphobia are prejudice against a person or group because of their different sexual orientation, gender identity, or gender expression.
Often homophobic language is expressed by people in order to mock others for acting a bit different.
Typically, homophobia is expressed amongst ones same-sex peer group which allows it to control what's socially acceptable for males and females. So as an example, if a girl wears trousers to the ball then she might be called a lezzie by her peers because in New Zealand girls are expected to wear a dress when they "dress-up". It's needless to say what a boy may be called if he wears a dress.
We have all been involved in homophobia and transphobia. We hear it, we see it, we do it, and we absorb it everyday.