I know that a few people have defended this already, but it absolutely infuriates me when people assume that teenagers and other younger people automatically have a lack of respect to go with their lack of years. We might well be percieved to be in the minority if we're polite, but my friend Luke and I get to the point where we jokingly fight to let people have our seats on buses and tubes; and my brother sparks up conversations with people at bus stops, just to talk to them about the weather or how long they've been waiting, and if they'd like his seat. I think that people of all ages can be disrespectful, and that it's disrespectul in itself to assume that people all of one generation, occupation or section of society are automatically rude themselves.
