I actually understand your friend because I can't see 3D effects, wearing 3D glasses jump-strarts my migraine and last time I've been to the mall I've tried the Nintendo 3DS for like 30 seconds.
I had to lay down on a bench and stay there with my eyes clodes tight.
So maybe your friend has never seen a whole 3D movie, but if they're as sensitive to it as I am and they've experienced it in any way, I fuckin' understand 'em.