I have a bad memory of the day I graduated from college.
What memories of your graduation are bad?
It's because my professor ripped into me that day for being not smarter than average.
While we all have events in our lives that we find difficult to recall, you may be experiencing an issue if this event is something that you ruminate on often. You shouldn't think of yourself as being not smarter as average and especially so since you graduated from college. Working with a mental health therapist may be useful in order to help you resolve these feelings of inadequacy.
I can't think of anything good so I'm going to work on something useful.
A therapist would help you focus on something useful. I really think you could benefit from therapy.