Iggy Azalea -- I Don't Have to Suck Britney's A**hole -- She's Why Our Song Bombed

Iggy Azalea has an excuse for everything ... and this time she's throwing stones at Britney Spears.

The song "Pretty Girls" bombed hard, despite a highly publicized music video. Iggy now says it's because Britney didn't get off her ass and promote it. Here's how she put it: "Its difficult to send a song up the charts without additional promo and tv performances etc. unfortunately im just featured."

Then Iggy goes in for the kill, saying, "My comment is factual, it applies to any song. I dont have to suck the womans a**hole 24/7 to be her friend, do i? bye girls."

Here's the thing. Iggy never says what Britney was required to do. She also has to know ... doing promotional interviews isn't exactly Britney's strong suit ... as in she's a deer in headlights.

And the song got more promotion than most.