A Mug with a Measuring Tape Printed on the Side
$12.99
This mug is eight inches tall. How do I know that? It has an accurate measuring tape printed on the side of it. You can use it to measure literally anything conveniently (such as your penis).
The only downside to it is that it can be quite hard to clean it because the inside is narrow and deep. Unless you have a bottle cleaning brush.
