Scumbag song meaning

This song describes a type of people that act incredibly friendly, come hugging you with a smile and telling you about their plans and about how great their life is. Most of the time they don't genuinely care about anyone, they just pretend to be your friend because they need someone to listen to their boasting. When they don't need you anymore they leave, but then come around again when they "run out of friends".

The narrator is irritated because he had to encounter one of those people again and so he's asking them why the hell they showed up, "what's the special occasion?" No one wants them around because whenever they open their mouth it's "the same thing again and again".

The song also appears in the American Pie - 2 Soundtrack (2001).