I think the fundamental concept behind relatively (spacetime has pliable dimensions) can be grasped at a fairly low level of education and without much understanding of physics nor knowledge of math... if you're willing.
Absolutely, I explained General Relativity to my uncles once, all of whom wouldn't have finished what you lads call high school, using a kitchen table cloth as spacetime.
However ICANT doesn't even refuse to understand the theories themselves. Instead, like with a lot of the creationists, we don't really ever get into arguments about the actual science, but instead get drawn into stupid discussions about what a webpage actually says or having him reference a site or a book stating exactly what we say as if it supports his argument.
Silly things like somebody linking to an article discussing a dinosaur fossil found in Europe, let's say, only to have the creationist poster say that there was no reference to Europe at all, only to France. Which starts the chain of posts:
"France is in Europe, AAARRRGGHHH!!!!"
I'm always reminded of a discussion here years ago with IamJoseph, where this had reached the point where people were posting things like
"You can stand on the surface of the Earth right? You agree with that, right?"
In short, we don't discuss the experimental support for a theory and whether it's actually strong enough, but instead spend three hundred posts trying to get somebody to agree to the possible validity of the concept of experimental evidence.