He's being sarcastic as a way of pointing out that he wouldn't know how to be any type other than ILI.

On a side note, if I had to choose between ILI and LIE for him, I'd say LIE. I'm that convinced he's not IP. But I really think he's Ti/Fe > Te/Fi. And if he is a Fe type (as opposed to Ti), I'd go with EIE > IEI.