A Prefect's Uncle by P. G. Wodehouse

It was perhaps only natural that Farnie, having been warned so strongly of the inadvisability of having anything to do with Monk, should for that very reason be attracted to him. Nobody ever wants to do anything except what they are not allowed to do. Otherwise there is no explaining the friendship that arose between them. Jack Monk was not an attractive individual. He had a slack mouth and a shifty eye, and his complexion was the sort which friends would have described as olive, enemies (with more truth) as dirty green. These defects would have mattered little, of course, in themselves. There's many a bilious countenance, so to speak, covers a warm heart. With Monk, however, appearances were not deceptive. He looked a bad lot, and he was one.

It was on the second morning of term that the acquaintanceship began. Monk was coming downstairs from his study with Danvers, and Farnie was leaving the fags' day-room.