Tell Ron that Halloween's over and he can take off the ugly mask. Say the same thing to Ginny, Filch, Percy, or anyone you find repulsive. (jk, I love Ron)
Hit Ron with a shovel (Another classic)
Scream "Fire!" and dump a bucket of water over his head. When he yells "Stop!", say, "It's not out yet! Do you want the Burrow to burn down again?"
Ask the Weasley twins if they do everything together
Making sure Molly is within earshot, bash Gilderoy Lockhart
Tell Ron how dimwitted you think Fleur is, and that he should go after girls with brains. In between fake coughs, say "Hermione"
Get Ron a necklace that says "Ickle Ronniekins" on it or stitch it on a maroon sweater
Threaten Bill with a haircut. A Muggle one.
(Also, I'm curious as to why we never see Charlie in the movies. Is he always in Romania?)