Can I tell my roommate that just because his family member died that doesn't give him the right to be a dick
Why do you think it's necessary to tell him that?
I think he shouldn't be a dick all the time, is all.
If this hasn't been going on for a while, I think you need to back off and let him grieve however he needs to.  If this has been going on for a while, I'd talk to him about how he's been acting rather than just call him out in an angry way.  You'll get a much better result that way!
I don't think it's necessary to act that way.
You're right it isn't necessary, but people grieve differently and exceptions should be made in the short term. If his behavior has be bad for a while then he may need some professional help. In which case it would be a good idea to gently bring it to his attention.