Hitting 50mph on a recumbent bike and then remembering there was a T junction at the bottom of that particular hill. It made me regret not opting for the Disc brake upgrade, but at 50mph it's a bit too late. I managed to slow (and could have stopped at the bottom) for the Give Way and roll out onto the valley road wondering just how hot the 20" front rim had got and whether the tyre would pop off the rim at some point.* It didn't but I spent a fair time scraping melted brake block of the rim before it stopped snatching!
*The first Mrs Byegad had done something similar on a Raleigh Shopper, in Durham and the report of the tyre letting go would, these days, have generated an armed response squad turning up. We never did find all of the inner tube!