word Okayest?!!

hello , i was watching a pictures of funniest Christmas Gifts
one of these gifts was a T-shirt Given to a girl written on it
" World Okayest sister "

What does that mean ? and what is funny about it ?

Thanks and Happy new year :)

Many manufacturers make shirts, hats and cups that say "World's Best Sister" or "...Boss" or "...Husband" or "...Teacher" or whatever. (Remember the scene in the Elf movie when Buddy saw a coffee shop sign saying "World's best coffee"? He took the sign seriously and opened the door so he could yell 'Congratulations!")

"OK" entered our language in 1839. It is an abbreviation of the deliberately misspelled words "oll korrect" ("all correct"). It is also spelled "okay" but most publishers prefer the initials instead. "Okayest" is not a real word. It is a nonce word, coined solely for printing on a shirt. My sister and I never get too old to tease each other. I can see why many men would want to make a gift of a shirt that says "You're not the greatest.....but you're the okayest."

And anyway, by definition, there can't be more than one "world's greatest sister."