Hmm… SO many to choose from, some not eligible for print
Robbie: Robbie-bob (good boy), RoBERT (horse in trouble), Robert-bob (horse in trouble, but with the potential to improve), Bobbert (if you were a stallion, something would be scheduled for removal), Baby Huey (you are a hunter, fer chrissakes, do you think you could manage to NOT step on at least ONE out of four trot poles?), Richard Cranium (yes, you WILL jump red flowers).
Raven was occassionally referred to as “RavenManiac”
Rebel is referred to as “Pony B” (Princess is Pony A), Ebs, Ebelreb, REBELDAMNIT and of course, “THAT Pony”
All of them are referred to as Sweet Pea when I am feeling particularly nice, and “generic dog food” when I am not (with the promise that if they are real good they may work up to Alpo).
Rivers is too new to have any good nicknames, but he does suffer from the same fate as the others when I am REALLY pissed: RobbieRebelRavenRivers, whoEVER you are STOP IT!!!