I find this thread really interesting.
I'm a big second-hander - not just clothes - everything. Just today for example I picked up a Brabantia bread bin and a paperback book from Oxfam (Only £2.99 for the bread bin! Bargain!)
But I get this love of the second hand from my parents, primarily my father but my mother isn't averse at all.
When I was a child we were reasonably well-off, but things like washing machines and dishwashers were always secondhand, and they had no qualms about accepting hand me down clothes for us. Most of my childhood was in second hand stuff, and it never bothered me.
(Although my mum's favourite tale is when I shamed them both at a family Christmas party and I showed everyone my brand new Mickey Mouse pajamas and told everyone "Look! They're BRAND NEW! No one has ever been inside them!"
I was 5)
They're both from quite poor, working class backgrounds, and have kept the mentality of repairing, making do and mend. This isn't the case so much anymore as they've got older - Mum is more likely to buy a new appliance or car, rather than a used one for fear of things breaking down / wearing out and she wants an easy life now. I will still search eBay and Gumtree if it's something simple she wants though, such as garden chairs or a mirror. She was recently over the moon at the beautiful set of Stag dining chairs I got on eBay for £6.50 
I sometimes think there's an inverted snobbery with turning noses up at second hand - not always by any means, but sometimes there's a detectable chip on the shoulder about it. One of my friends is like this, from a family with a very similar background and upbringing to mine - she's both awed and disgusted by the fact that 95% of my possessions are second hand, and as a result, I can afford nicer things than she can. Meile washing machine, Gaggia coffee maker, Kurt Geiger shoes, Brabantia bin, Le Cruset pans, Denby crockery... the list is endless. I would never ever pay the cost of such things new, but I can second hand. For me it's a no brainer!