As far as getting pissed, just remember that any organization "begging" for money from the common people is doing so because they need it. They don't get millions or billions in tax breaks. We never see fortune 500 companies begging at the grocery store because they do their begging on Capitol Hill and essentially take our money without asking us to put it in a jar. It's estimated that fortune 500 companies have $1.6 TRILLION in offshore accounts so they can avoid paying taxes. When I see a kids' charity or a community nonprofit asking for donations, I get angry that they have to do that while stupid companies like Facebook find loopholes that allow them to pay NO taxes. So if we're talking anger about money-grubbers, I'll aim mine toward the truly greedy and not the needy ones trying to do good in the world.
I understand all that, and i do contribute when i can.. But when i go to 4 different stores and get asked to donate 4 different times, when i enter, when i check out, or when i leave, then feel like a jerk because i say no, i've already donated 2 times today, sorry it gets irritating..