I'm going to start dating a ex of a friend
Do you think this will make your friend upset?
I am not concerned about him getting upset. He is a jerk.
It is a free country, so date who you want.  But, it is frowned upon to date a friend's ex.
He's just a douchebag and I will probably blast him.
I just think you should let your friend know before you start dating them. This can be something that could make your friend upset if you are not careful. Being honest with them is probably the best way to go about it.