Tsuruya is such a gigantic cocktease, that's why.
“Where have the both of you been? Ah forget it; it must be due to some reason that you can’t tell me, right? Don’t worry, I’m not such a busybody anyways. Why, Miku--- I mean, Michiru, you’re filthy all over! Let’s go take a bath, shall we?”
Tsuruya-san said the above in a single breath.
“It’s cold outside, isn’t it? Come on in and have a bath first! That’s right, a bath! Kyon, would you like to join us too? I’ll scrub your back for you nyoro~”
Even though I was moved by the suggestion, I knew that Tsuruya-san was just pulling my leg. Haruhi loved to blurt out some serious suggestions while putting on a look that suggested she was just kidding. Tsuruya-san, on the other hand, loved to crack out jokes while putting on a straight face.
“I think I’ll head home. Well, please take care of Asahina Michiru for me.”