why is that supposed to be funny?

The ones that are feeding them are the ones that ignored them.

These guys bought a hot meal meal for a couple of people, real food, no tricks or humiliation, and they sure as hell weren't ignoring them. If they think that is funny I hope they get a good laugh everyday, and maybe more people will join in the laughter.

You will notice when he offered his credit card they did not take it.
And that is because by saying they were the cops it influenced the ones that ignored the homeless to offer to give it free cause they thought they were giving it to the cops...
That is pretty funny to me....willing to give to those that don't need it but ignoring those that do.

You get it.

It's subtle, but the pizza delivery guy thinks it's some kind of undercover operation he's participating in, and the homeless ones have a much luckier day than they've had in awhile, I'm sure.

Not laugh-out-loud funny, but a clever set-up with a great pay-off. More "pranks" like this one, please.