What does Paul Avery tell the coffee guy after the coffee guy calls him a "drunken reprobate"?

As per my comments above, I've tried to listen carefully many times to what Robert Downey Jr. is mumbling in italian in the following scene (at approximately 43:42 as suggested by the OP):

and I agree with the preceding comments that he probably says "minuscolo grazie".

My best guess is that the first italian word, "minuscolo", might be referred to the character's name Shorty, played by the actor James Carraway, although "minuscolo" is not a very accurate translation of the original english word. In italian, when teasing someone about his height, we would say "Corto" or "Tappo" while "minuscolo" actually means "tiny" or even "lower case".

But the poor choice of words might also be due to the fact that, as suggested by Walt in his comment, Robert Downey Jr. might have just improvised the bit. This is also corroborated by the fact that there seems to be no trace of the dialogue in the script.

The second italian word, "grazie", is much easier to understand and so the corresponding english translation of "minuscolo grazie" would be "Thanks Shorty".

Also, the fact that the sequence of the two words is reversed by Robert Downey Jr. (as in english we would say "grazie minuscolo" and not the opposite), doesn't help much.

I've also listened to the italian dubbed version of the bit, in the hope of better understanding the original meaning, but it didn't help much, because the phrase has been translated in spanish, and I'm almost positive (I'm Italian and don't know much of spanish) that he says "por supuesto, gracias", which translated in english should mean something along the lines of "of course/sure, thank you".