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
When Brian knows I’m right but wount admit it
L- I love you the most
B- I love you mostest
Grater than most
Example:
Girl friend: “I love you most”
Boyfriend “I love you mostest”