Ha! That's great. I think "not the most challenging material" is actually a lot better than really hard stuff. Because that usually just brow-beats you into thinking you don't understand anything.

my co-workers thought I'd lost it when we got a shipment of Peppa toys and I started speaking to them in French.

Would they have been less bothered if you spoke to them in English, I wonder? Also, this is assuming they believed you to be sane to begin with. Bold statement :P