Aha. There's one for the saddest, why not the best? If there's already one, forgive me.
For me, that would be Ojamajo Doremi Na-i-sho! 01 (A Messed Up Cycling Trip - The Boys Secret). Allow me to type out the subtitles:
Doremi: This incident started one week ago.
*scene shows a stack of report cards*
Seki-Sensei: Next one is Harukaze Doremi.
*scene shows Doremi standing up quickly, and Momoko is leaning back in her chair, mouth open (she probably got bad grades. Poor Momo-Chan!)*
Doremi: H-Here!
Doremi's Mother: Doremi! If your grades improve, we can have steak!
Doremi: If my grades have improved...we are having steak tonight!
*Doremi walks to Seki-Sensei*
Doremi: We are having steak tonight! Steak...steak...
*shows scene of two cows, one moos*
Seki-Sensei: Here you go.
Doremi: Thank you.
Doremi's Mother: If your grades improve...
Doremi: We are having steak tonight!
*scene shows two cows, with their backs to the screen, and it then shatters*
Doremi: *a splodes* *falls on floor*
Seki-Sensei: H-Harukaze?
Doremi: My grades slipped...
Seki-Sensei: Harukaze, are you alright?
Doremi: Sensei! I beg you!
Kotake: What is it, Dojimi?! Did you get a "try harder" in every subject?!
Doremi:
KOTAKE!!!!! My...my...my steak!
Seki-Sensei: *grabs a hold of Doremi* Even though I don't understand what's going on...but you'll have to try harder next semester, Harukaze.
Doremi: *groans* Yes ma'am.
Absolutely the best scene ever.
EDIT - ZOMG. How can I forget? Now, let's see if I can get this right. Motto! Ojamajo Doremi 101 (Doremi's Stormy New School Year)
I cannot describe it's amazingness (and the funniness).