Junior was about to tap his foot impatiently until Luigi actually complied with his request and he got to wear the hat. Junior was happy to have something like this, it must be something special if he got to wear it! He'd keep his promise to keep it just for tonight... maybe.

"Hu hu! Don't worry, I'll take good care of it!" This was also a great chance to try out his human form for a while, he'd be sure to enjoy this.