Person 1: I love you.
Person 2: I love you more.
Person 3: I love you the most.
Person 4: I love you the mostest.
mostest can be used for when you're trying to find a word bigger than most but you can't think of anything so you need to use mostest.
Its a word of endearing. When your significant other says something along the lines of "I love you the most" you can say "well, I love you the mostest"
"Hey babe, I love you so much"
"I love you most"
"I love you the mostest"
When Brian wount admit im right
L-i love you most
B-i love you mostest