This is an easter egg in Five Nights at Wario's 3. You can find it when you hide in Living Room 3.

The Diary

"Dear Diary, I actually like my new Job! Sure, Wario and Waluigi can be a bit hard at times, but, well, thats how they just are. They only have money on their mind, I guess. But still, I've had a bad feeling lately. Like, it feels like something terrible is going to might be the fact that Bowser has been lurking around the building for days now. Because of this, I hide in the cabinet in the Tool Storage when I have some spare time here at work. Nobody really goes in that room anymore, so nobody knows i'm in there! Feels kind of safe to me... so yeah, I tend to hide in there pretty often. Atleast until I stop seeing Bowser. I'm sure i'm safe in here. Toad, March 23rd, 1991."