I'm going to crank my sub woofers with my girlfriend's son in the car
Why would you do that?
I just want to irritate her son
Do you think it's okay to intentionally irritate the son of your girlfriend?
Maybe I'll show him how much music he can take before he starts crying.
It seems you are already aware of what you're doing is going to harm the child. Do you think its okay to hurt children in this manner? If the child tells your mother what you did she will probably break up with you too.