About T-Shirt Design
Some shirts are funny because they are super clever. I Think You know what I am Mad About Tee is funny because it is simple and relatable. The everyday humor angle gives it a little extra personality without making the design too busy.
It makes sense for birthdays or holidays, especially if the person already likes this kind of humor. It has the relaxed feel people usually want from novelty shirts without getting too complicated.
The whole point is to get a laugh, and the shirt does that without making things complicated.