Something said to a girlfriend, boyfriend, wife, husband, best friend, mother, father, sister, cousin, life partner, etc. to describe that they are above and beyond the best when in a competition of who is better and you want them to win.
Person 1: "Awww sweetie your'e the best!"
Person 2: "No no no baby, your'e the bestest"
Person 1: "Oh yeah well you're the bestest-EST!"
Person 2: "That's not a word silly."
Person 1: "Yeah it is, look it up in a dictionary."