I recall occasionally asking a boy for his own gym shoes, but only when I could see he had a suitable one. I remember once telling each of the three boys in front of me to supply a slipper, and then choosing the most suitable. Flat smooth soles were always preferable to ribbed or patterned ones, and also fairer on the victim’s bottom!
A few colleagues, even if not involved with PE or Games, had acquired themselves a favourite slipper which they kept in a drawer or cupboard, and some gave them names including Tonker, Mr Slap, and Sammy the Slipper.