'Overlook' in the sense of forgiving, or letting something slide. All the words I can find that seem to be very close in meaning--大目に見る、不問に付す、聞き捨てにする、罷り通る--don't seem to be used in conjunction with にくい (or づらい), which is something I really want to use to get across that it's hard but not impossible. The closest thing I can think of is 許しにくい, but it lacks the indirectness and slight scorn that comes with the other verbs.
Context: "His actions are getting increasingly hard to overlook."