What's the fitting process for Vibram Five Fingers shoes?

My stepson says “No socks.” They’re in European sizes, so the best thing to do is try a pair on in person for fit and then buy them online. For reference, a 43 is about equivalent to a mens’ 10½ US size.

I have seen either sock or sockless. It all depends on what you are doing and how often you want to wash them.
As for fitting, here is a good link on fitting
Here is a link to socks that go hand in hand errrr foot in foot with them.
Injinji Footwear

I’ve seen both sock/no sock. I don’t have any toe socks anymore so I do no-sock. I’ve been getting blisters on my toes and heels so it would seem breaking-in is necessary. They slip a little bit when I walk / run so maybe that’s the problem. I’m not totally sold on the 5 finger thing yet, either. The soles are too thin for me so far on concrete and asphalt. On grass they are nice, but you really have to watch out for rocks or bear the pain of stubbed toes.

When I bought my VFFs, I tried them on without socks. I recommend you do the same.

I prefer to wear the Injinji toe socks with my VFFs. For the first few weeks after purchase, I wore them without socks, but eventually found that my feet would sweat (it’s hot here) and my VFFs would stink. They’re machine washable, of course, but that’s a pain. So I got the socks and that has helped with the sweat/smell problem quite a bit.

If this will be your first pair, I strongly recommend that you try on VFFs at a store to ensure you can fine tune the fit.

Note: if your second toe is longer than your big toe, then you can’t wear VFFs.