I was telling my son (~3 at the time) about the days of the week. I asked him what day it was today and he said Friday. I knew exactly what his reaction was going to be next so I started recording the interaction on my phone.
I asked him what day it is, he says "Friday", I let him know "well actually buddy, it's Tuesday", and a meltdown began with him yelling "No, not Tuesday!"
I'm sure every adult has shared that feeling, nothing ruins your Friday like realising it's Tuesday.