Ah, yeah. I WAS that shitty friend. It actually takes a fair amount of effort, cleverness, observation and timing to do it right. But with enough dedication, you can make your friends' lives a living hell.
It's a calling.
@Randomizer
Considering FMC was just slightly possibly maybe somewhat upset about MC's adamant denial, she may have intentionally looked for a pile precisely to ruin MC's new shoes, even selling her own sole.