I decided to take his umbrella.
Why did you want to take his umbrella?
Because he's been mean to me and he's taken things from me in the past.
Taking something that belongs to him as retribution for past wrongdoings is in appropriate. You should talk to him if you're having an issue with his behavior.
I don't have time to talk to him about it.
I know that you're frustrated with him, but try not to get into a conflict with him. Taking his things to get back at him will escalate your issues and turn them into a larger problem between the two of you.