I've never 'got'

Heat and exertion - the body gets extremely distressed and things come out one end or the other.

I've raced in extreme heat (42 degrees at IM China being the worst), and am not very good at it. My body doesn't like what it's being asked to do and doesn't want to deal with digestive functions, so it tells me I don't need any food or water. I've ended up on a drip 3 times at events before I sorted out my approach to nutrition (ignore your body, it's just trying to sabotage you so it can have a nice lie down in an ambulance).

Running has a well known tendency to get the bowels moving even in non-extreme conditions, so adding extreme conditions can be alimentarily explosive.

@HatBeard once tried to organise a "coffee run" - a run with stops at various coffee shops. Can't remember if it ever happened, but there was a broad consensus that the participants would need to wear nappies.