So I was watching the DC (again) and I was thinking that after Lorelai sings her song to Luke, that they chat briefly. Lorelai mentions the return of the blue hat, but Luke just shrugs it off and says he's wearing it because the black hat suddenly disappeared and he has to wear a hat in the diner for sanitary reasons. Lorelai is discouraged because she really feels that Luke was trying to tell her something with the return of the blue hat and out of self-protection of her pride, when Babette and Patty asks her about the karaoke song in the next epi, she basically shrugs it off and passes it off as insignificant.