You don't go toe-to-toe into a fight with that person. You can look for a Kryptonite-type weakness, but outsmarting him can mean other things, too. Trick him into thinking you're someone else and escape. Lead him into a trap -- get him to follow you into some place where he's at a disadvantage, or into a dangerous situation. Stay out of reach and frustrate him into making a dumb mistake that will get him killed. Work against him mentally -- if you have information about this guy, talk to him, get him to feel insecure about his decisions, make him doubt he's doing the right thing by attacking you. Or lie, and bluff him into thinking he needs to let you live. Or just genuinely talk him down, find some way to emotionally reach out to him and soften his approach. "Find their weakness" can be psychological, too.
Ultimately it depends on what you want here as the author. If you want an awesome epic fight, you probably want to find a Kryptonite. If you want to emphasise the feeling of your character as the ant fighting the boot, you'll probably want something more risky and scary, like running away and leading him into a trap.