Originally Posted by
rogueboy
Depending on the context (who isn't understanding you, and who's saying you can't say they aren't understanding you?), you could be in a position where you're just stuck with babying them (if it's a supervisor, for example), or they may just be an oversensitive moron (if they're a student). Either way, you might be able to strike a balance between "you aren't understanding" (which blames them) and "I'm not explaining properly" (which puts the blame on you). Perhaps something along the lines of "something seems to be getting lost, let's try again" (which doesn't blame them, but also doesn't admit fault).
That being said, I'm not sure why going increasingly towards the most basic it can be isn't allowed, which is what makes me suspect it's someone being oversensitive (which, if it were me and they weren't a boss/supervisor, I'd completely ignore and just continue simplifying it and telling them that they're missing the point).