I believe "oppression under color of law" is the correct term if the TSA supervisor was not correct about him giving up rights by buying a ticket. That claim doesn't hold for a store saying "we reserve the right to search your bag on exit" and I don't believe it holds for air travel either.

Denying boarding is one thing. Just as a store can kick you out if you refuse to check you bag at a bag check. But the bill of rights is pretty clear about when you can search someone and deciding you don't want to fly doesn't exactly give probable cause for anything.