Do you think my gf getting upset about photos I like in Instagram is laughable and very 'high school'? I sure do!
Why do you think of it as laughable and high school-like? I'm shocked to hear something like this.
I know she has a huge crush on another guy.
Although you may disagree with how your girlfriend feels, you shouldn't disrespect her feelings by laughing at her. Doing this will only make it appear that you don't care about her or your relationship. Instead, talk to her about how you feel about her getting upset and what your social media actions mean to you.
No, I'm going to ignore her feelings and keep doing what I want.
Emotions from people can be complicated, and not always stable. Bear with her, she might be going through a stage, and just make sure you talk things out when she is ready. Ridicule is a form of abuse, don't go there.