I'm going to pour gasoline on my roommates plant
Why would you pour gasoline on your roommate's plant?
The plant really bothers me and I want to get rid of it.
I understand that the plant is bothersome to you but it's not right to ruin your roommate's possessions. You should take to your roommate and work out a compromise. Destroying something they own is not the right way to handle your problems.
I don't want to live with it in my room. I might light the plants in my house on fire accidentally.
You and your roommate might not be a good match and maybe one of you should move out. You could get in trouble for ruining his things and you could set the whole place on fire.