I've been to one of these at my kids nursery sports day. I didn't really know what to expect beforehand and turned up in work clothes and leather shoes.
The mum's race went first and it looked fast. The face was fairly close as the usual Olympian bobsleigh mum wasn't there. Then it was the dad's race. I noted that most dads had gone for the subtle "normal clothes but running shoes" look, but some were fully ready in shorts and t-shirt on what was quite a breezy and cool day. Hmmm more serious than I thought. Anyway I got a bad start, but came through for 3rd I think. My kids were a bit disappointed, but it wasn't a total embarrassment. I'm going to aim for this kind of mid-table mediocrity for future sports days and hopefully never raise the expectation of a win for my kids whilst not being too embarrassing.
Its a fine line.