I'm planning to go to a gym to make fun of people there.
Are you kidding? Why would you want to make fun of people at the gym?
It looks like a good way to spend my time.
This is not a good way to spend your time. You shouldn't go to a place and make other people feel uncomfortable when they are trying to better themselves. They could be self conscious as it is and with you making fun of them, it will only discourage them to keep trying.
I just want to have fun and I think it's hilarious.
It's not funny to the people you are making fun of, I assure you. That's a really awful way to spend your time, you should be encouraging these people instead.