Ruth McWilliam wrote:
I asked him if he was going to let me do the backstretch, then sensei clapped so I turned away from him and scooted back to the side of the mat without bowing (which I know was rude, but the 4th kyu was rude first)
I know I could have gotten him to move by aiming my knee at his testicles
I don't think your uke was rude. He's the sincere and honest uke that is lacking in some Aikido dojo.
Your line of thinking like "knee to his fork" isn't Aikido IMHO. Your honest uke certainly wasn't a jerk.
"Ki" in Aikido isn't stressed enough in some Aikido dojo. O'sensei showed "ki" to us by demostration of several uke pushing him physically whiile he's standing/siting stil.
Strength and powerful are good thing to have in Aikido. Muscle is only a part of the "strength". If you only demploy muscle in Aikido, you ignore the other more important element in strength. I'm student in search of acquiring the "other elements". Mike, Rob, Ellis and Ron have written quite a few posts about Ki, you may want to look it up.