Look, I'm sorry that your job blows. I really am. It's 90 degrees, and here you are, standing in direct sunlight with your clipboard, tasked with somehow obtaining money from people who find you irritating at best. You wave and jump in front of one stranger after another, delivering your opening line with a relentlessly perky attitude — and 90% of us just keep walking. Then you've got the assholes who scold you for interrupting their afternoons, and (worst of all) the sweet elderly people who actually stop, let you talk for 10 minutes, and then decline to sign up. It must be terribly demoralizing.
And you know, maybe it's rude to mumble "sorry" as I walk past you without slowing down. But don't you think it's also rude to approach someone who is sending "nooooo, don't talk to me, nooooooo" signals, and then force me to either a) waste everyone's time by stopping, or b) feel like an asshole when I coldly walk away from a fellow human being who is asking for my help. Not to mention your opening pitch, which forces me to either get sucked into talking to you, or say that no, I can't spend sixty measly seconds of my privileged existence saving the earth, helping the children, or supporting gay rights.
I realize that if you don't coerce enough sympathetic suckers to sign up for recurring credit card payments to your bloated, self-enriching organization, you will get fired. And that makes me feel a little bit bad for you. But if you think about it, wouldn't that be the best outcome for everybody? I'll be able to buy lunch without encountering your intrusive solicitations, and you'll have to move back in with your parents, which will give you an opportunity to bond with them during their golden years. Mom and Dad won't be around forever, and one day I bet you'll cherish the memories of helping them out with chores in exchange for food in your mid-20s. Sure, this might not be what you imagined post-college life would be like, but is it really any less appealing than begging strangers for money in the heat?