That's pretty funny.
My oldest child had a very short shower the other day. When asked how it was possible to have washed her hair in such short time, she indicated that she didn't wash it because the water was freezing cold. Her younger brother had used all the hot water, she alleged..
We've had a tankless water heater in the house for 7 years. That's almost her entire life. I have no idea where she learned that "used up all the hot water" is even a thing! Maybe at grandma's house.
It turns out she had the single-handle valve operation confused and had turned it to full cold!
I think Tankless LP Water Heater
may be the thread nat_ster was searching for. His list of pros and cons is in this post