... who apparently purloined a pair of DS1's then-brand new school trousers (M&S, don't know if it made them more attractive??) back in October, hung onto them the entire school year, and then sneaked them back into the classroom where they were found by the teacher, who put them into DS1's drawer. She was able to do this because they still have the name-tag sewn into the waistband.
They've clearly been washed and worn and washed and worn all year and are in a right state, and have massive holes ripped in the knees. So basically some parent - presumably someone I've chatted to while waiting in the playground to collect our DC - has used these an entire year, seen the name tag every time she washed them or helped her son into them, and only returned them to class when they were essentially unusable. 
It's not the trousers. I was initially a bit pissed off to lose a pair (it happened at PE, DS1 and the rest of his classmates (Reception age) are basically a bit rubbish at keeping their clothes in neat piles so a fair amount of swapping does go on, but most stuff is marked and gets returned. The time this happened, he came home in unmarked trousers and presumably the boy whose ones he had, went back in DS1's.) but chalked it up as one of those things. It's the bare-faced, brazen 'fuck-you' of the parents who've used them all year and not even bothered to cut the label out, before returning them because they were no longer usable. I don't think they came from the lost property box (for example, were used by a teacher as emergency trousers) because she'd
have spotted they were marked and returned them to DS1's tray.
I mean, even if you're hard up (and we're not rolling in it ourselves) you can get trousers in multipacks from supermarkets for a couple of quid, and failing that, there have been school uniform sales each term where everything is 50p. It really makes me feel creepy that someone I've been chatting to in the playground has, all that time, been thinking 'I've got your son's trousers'. 