If a Japanese person says "How are you?", reply with a monotone "I am fine, thank you, and you?". This was probably the first English they learned back in 7th grade. Sometimes they actually get the joke.
Ask them what "ee to" means. When they tell you, ask how it is different from "Ano..."
Say "chotto gomen nasai" for minor infractions. When someone explains that this isn't a normal thing to say, ask why "chotto sumimasen" is okay and watch their head spin. For that matter, ask them about "chotto nai": "it doesn't exist, a little bit".
When you're about to cross a 1-lane road with no other cars for 500 meters in either direction and there is still a mob of people waiting for the crossing light, proceed across without breaking stride. Bonus points if there are mothers holding their children back for whom you can provide a bad example, and further bonus points if anyone who was previously standing there follows you.