A comeback for when someone questions your style, taste, or decision making. It can be used when the actual reason is too embarrassing to admit, would cause you to lose street cred, or you dont know why and want the other person to shut up.
Why are you going to see Bareback Mountain? Dude, that's just how I roll.
Why are you wearing a shirt with an amusing slogan, a trendy blazer, 300 dollar ripped jeans, and haven't shaved in a week? That's just how I roll.
Why are you ignoring me? That's just how I roll.