Jason Biggs is getting trashed for joking that he now wants to sell his Malaysia Airlines frequent flier miles ... but he's not backing down.

Biggs tweeted shortly after the crash of the 777 jetliner, "Anyone wanna buy my Malaysia Airlines frequent flier miles?"

People went nuts on Biggs, saying, among other things, "Go f**k a pie you piece of s**t. You're such an attention seeking f**king whore," and "You'd laugh if your kids died in a plane crash?"