Wrong Says

When I went home from my course, I was very confused because of many subject that learned on the course. I tried to concentrate and chat with my friends, but it didn't succeed. So I stop talked and didn't do anything for a few moments. When I wanted to get off from public transportation, I should said "Kiri!" but I said "Assalamualaikum!". Oh, God! It was so embarrassing. Every people in that car were laughing and watching me. I will never forget this moment...