Irie Shoichi is a very smart individual. Over the course of his life he's made frighteningly hostile computer programs and changed the layouts of buildings with the ease of an expert tetris player and set complex time travel schemes into motion. He's even helped save the world once (though he also helped cause the destruction of countless others, but that was completely unintentional and something he would rather not discuss).
Some call him brilliant. Others may even go as far as to call him a genius. Gokudera calls him a bastard though, because he simply cannot let him live down the fact that he helped ruin nearly every world in the universe and forced the Tenth to fake his own death just to fix everything.
Irie himself, however, refuses every compliment people give him in regards to his mental prowess. Because even though he has accomplished many things and has had a host of impossible experiences, he can't allow himself to think he's as smart as others say he is.
Not until he figures out how on earth Spanner can build multiple moscas, fine tune Vongola's machines, and keep that one section of hair curled perfectly while still always managing to get a full night's sleep.
Of course, Irie also doesn't know that Spanner spends many nights laying in bed, wondering how the brunet can accomplish the feat of falling asleep while in the midst of getting undressed.
Spanner calls him a genius because that is very, very impressive.
A/N: I wrote this for a friend, but I wanted to post it anyway. I was under the impression that Spanner did not sleep at all until Tsuna actually asked how he and Shouichi were feeling (right before they all played Choice, I think) and someone mentioned that they were resting.