A pedestrian is someone traveling by foot. If you're walking, you might get angry at the drivers who don't stop so you can cross the street. But if you're driving, you might fight the urge to run over those annoying pedestrians!
Pedestrian comes from the Latin pedester meaning "going on foot" but also "plain." As a noun, it's someone walking around — sidewalks are for pedestrians. As an adjective it means "lacking wit or imagination." If someone calls your new poem pedestrian, they mean it's dull. If you want to impress your friends while also making them feel worthless, mutter "these people are SO pedestrian," at a party, loud enough for everyone to hear.