So you're pairing up, and it's your partner's turn to try the technique you're learning.
You do your best to make sure you are not actively resisting your partner, but at the same time, you're not being so passive that you're helping him make it work.
It's your turn, and you go to do the technique, and your partner immediately counters what you're trying to learn. You try again, and your partner changes her stance around so that the direction you're supposed to go won't work. You try again, and she has a death grip or is using all of her strength to oppose what you're trying to learn. Since you're just learning this technique, you don't have any clue how to cope with this behavior.
Frustrated, you're glad when the instructor yells "switch partners!".
The next partner is the opposite of the first. He noodle arms and goes limp, he doesn't resist whatsoever, and he falls down the minute you touch him with any kind of energy. It's like trying to train with the wacky inflatable tube man.
You got paired up with the two most common examples of THAT GUY: The Exceptionally Bad Uke.
The Exceptionally Bad Uke is the person who makes certain that no matter what, you are not going to learn what is being taught correctly. You'll either believe it can't possibly work for you - because of the first type (the "Hard" Exceptionally Bad Uke) actively resisting you before you understand what you're going to do, or the second type (the "Soft" Exceptionally Bad Uke) giving in so quickly you know you aren't understanding the technique, either.
You run into Exceptionally Bad Uke at seminars a lot. Often, the "Hard" version is trying to uphold the honor and reputation of himself or his school, or, he thinks he's supposed to do that, so that the training is "realistic". The "Soft" version is trying to be polite and helpful (not realizing that what she is doing is as bad as 100% resistance).
Personally, I find the "Hard" version more annoying. I'm always worried that I'll hurt the guy, because this kind of hard resistance can lead to that sort of thing by accident. Or, in frustration (especially when learning disarms) I'll use a softening up technique to get the disarm, and that often means an unexpected strike in places that are uncomfortable.
The "Soft" version is less annoying but might be the more dangerous, as you believe you've learned the technique properly when you haven't because the Exceptionally Bad Uke is so determined to go with it, you get a false sense of confidence in what you know.
Either way, trying to learn while paired with the Exceptionally Bad Uke is a miserable experience when you're trying to figure things out in martial arts classes or at seminars.
Tell me your stories of the Exceptionally Bad Uke. Have you, yourself, been THAT GUY? Let us know in the comments!