Learn English – Meaning of Port and Dunnin

You have two somewhat conflicting answers already:

• Wichita Steve, understanding condescension in its original sense, says that Eames acknowledges Arthur's "courtesy" in praising an inferior.

• user3169, echoed by Toby Yuretich, understands condescension in its usual modern sense and says that Eames pointedly rebukes Arthur's "patronizing behavior".

I think both of these readings are true and pertinent.

Arthur and Eames have in fact the sort of friendly rivalry in which each regards himself as the other's superior in some respects but values the other's superiority in other respects. This relationship is sustained by adopting a teasing tone toward each other, in which genuine regard is disguised as apparent mockery.

So Eames' response actually operates on two levels. On the overt level, Eames' use of condescension subverts his appreciation and transforms it into irony: he dismisses Arthur's compliment as patronizing. But on the covert level, both Arthur's "condescension" and Eames' rejection are part of the 'game' they play; in fact, both Arthur's compliment and Eames' appreciation are genuine.