@CCY: I peeked ahead for a few dialogue screens. Shizuma explains it in a deadpan, matter-of-fact manner, throwing in some criticism on how Tita should have closed her curtains. If he remains silent, though, Tita refuses to elaborate, but Makina very accurately guesses what happened.

Since it's early in the game, and odds are that the first decision doesn't matter, I say go with chaos theory and pick the option that's the most ridiculous and most unlikely to be picked by a standard overly-nice harem lead. I find trying to smash that stereotype more entertaining and sometimes more rewarding.

Unfortunately here it's grey area because "explain it yourself" can either mean explain it 1) stammering and apologizing the whole way (likely) or 2) explaining in a wonderfully sarcastic, witty fashion (better, but unlikely), but I vote the bottom. I'm sure Tita will do a great job explaining it herself.