Mr. Kapasi's a lover, not a hater. It just takes a little effort to crack his jaded exterior. Which is what Mrs. Das does when she points out that his second job as an interpreter is so romantic and important.
All of a sudden, Mr. Kapasi warms up, and not just a little either. He goes from zero feelings for Mrs. Das to major fantasy levels about her legs, her future correspondence with him, her clearly loveless marriage to Mr. Das… all in the span of a few hours.
But we all know that what goes up, must come down, which is pretty much what happens to Mr. Kapasi's affection for Mrs. Das once he finds out that she's a total lying cheater to both her husband, her kids and her lover. In fact, he's kind of like a brutally honest therapist when, after he's heard her spiel, he asks her, "Is it really pain you feel Mrs. Das, or is it guilt?" (IM 161). Mr. Kapasi: the guy who will show you who you really are, as long as you can handle the truth.