I realise it's hard being told to ignore something like that - it feels bad for self-esteem. I remember parents and teachers constantly telling me to just ignore silly things, but it didn't feel right not defending myself. Even now, if I do decide to complain about something, or tell somebody that I'm not happy with what they're doing, it takes me a lot of courage to do so.
I was bullied a lot up to year 7 - after crying my way through primary school, which attracted yet more teasing, I became so adept at ignoring remarks from others that sometimes I didn't even realise when someone was trying to insult me. I was once genuinely surprised when one of my friends said to me "but that teacher used to pick on you quite a lot, didn't he?" I hadn't even realised. But it was hard. Even when I was in year 12, there was one year 7 pupil who would mock me whenever they met me, I seemed to attract it! Ignoring it got me through senior school, but it didn't do much for my self-esteem, and I did have to learn how to be assertive as an adult later.
Although any kind of bullying is horrible, I think a difficult thing for anyone to learn is if and when it's worth taking action, i.e. replying, or reporting it. The mocking shoes in itself might not be worth replying to, but if the shoes were being stolen that would be another matter. We all know on MN about wolf-whistling builders, to which the usual MN reply is: report it to their bosses, because these days, they actually do something, and there's not likely to be much comeback for you; but you might not try shopping a local well-known gang leader to the police unless you really knew what you were doing. I was reminded of Geri Halliwell wanting to complain to the press about something they'd said, but being told "you'll only turn it into a bigger issue".
Nowadays if someone shouts out of a car window, or sounds a car horn, I don't flinch at all, or even look, which is sometimes a problem if it is someone I know who wants to offer me a lift!
My brother once refused a pair of brogues similar to what you're describing while shoe shopping, saying "they're Mr Bean's shoes". He got called Mr Bean a lot. He sometimes said in a bored voice "who's Mr Bean?".
I'd agree with the saying nothing to the bullies, but perhaps explaining that in other circumstances, you do speak, for instance if he was being regularly picked on by a teacher, or serious bullying such as things being stolen, or physical harm. Even replies such as "they're just shoes" might provoke the shoes being thrown around the playground, with the taunt "they're not just shoes now, are they?" as he tries to rescue them.
The classic MN "did you mean to be so rude" is very different; in most of the circumstances advocated by MN, the person who is rude is not expecting a reply at all, which is where the shock value comes in; whereas school bullies are hoping for a reply that they can mock.