Casually place a grapefruit in the fruit basket first. If you see a gleam of passion in his eyes staring at the glorious fruit, step two: poke him with a needle while he's not paying attention. If there's no reaction, offer him a glittery thong and some pro-tan just saying that you thought he might like it. If he does, get him a plastic trophy saying "Son Of The Month"" or something along those lines. An ecstatic reaction means you probably have a potential Mr'O living in your house.