SADAR - Have a backup Valkyre GF that will roar whenever the SADAR fires and hits.
Pyro - Have both someone to stun them, and a rav to murderize them while/after they are stunned.
Scout - Turn up gamma or contrast or something. I am completely blind to them.
GL - Just go right next to them and dare them to nade themselves. If it hits, it hits you both. And it stuns him far longer than it stuns you.
Sniper - Bodyblock his shots until he runs out of ammo. Then he is truly useless.
Edit: I forgot about SHARP. Go spitter and do the ranged acid vomit on all his mines. You can then go next to him and drink the tears of his face in real time.