The expression is "Verreck(e), Du Aas". "Verrecken" means "to die miserably".
"Aas", literally "carrion", "dead animal body", is a very traditional
and a bit old-fashioned insult, primarly for a dishonorable, malicious, perfidious person.
Combining both, "Verreck(e), Du Aas" is a curse. Something like
"Die, Motherfucker". If you read it in early 20th century texts,
it means exactly that.
That usage is outdated, though.
If you hear it today, it's most likely a humorous alternative for
"Gesundheit!" when somebody sneezes.
This is a bit similar to wishing "Hals- und Beinbruch", or in English,
"break a leg": There are old superstitions that the gods of fate
may intentionally do the opposite of whatever you wish, so in order
to fool them, you invert your wish yourself.