He was from Oklahoma...
"Everyone has a plan until they get punched in the mouth."
First hate (and really only hate) will always be Philadelphia. No exceptions.
The key point in your post is, "I might have been a kid during the Aikman era". Which means you most likely remember the Superbowl championship in January of 1991, which helps.
Had you been a kid during the 1970's Roger Staubach era, when the Giants stunk. You might have a stronger sense of hatred towards the Dallas Cowboys.
For the record: The photo doesn't kill me. I was going for a little humor here, when I saw the photo on the internet last night. Mickey lived in Texas during his career, so I'm not shocked to see him wearing a Cowboys shirt. I probably would've posted an identical thread if I saw a photo of Eli wearing a Boston Red Sux shirt.