"Frack off" is a way of saying we don't want people to use a certain type of drilling called "fracking." Fracking is when people pump a lot of water and chemicals into the ground to try to get gas or oil out. This can be bad for the environment because it can pollute our water and air. So, people who say "frack off" want to encourage others to find better ways to get energy that are less harmful to our planet.