Taken from that link above:
Excuses: This is the holy grail of passing someone – they are so deeply humiliated by your passing that they want a chance to explain themselves, usually by saying something about being at the tail end of an all-day ride or being told by their coach they must keep their heartrate under 80. When this happens, smile knowingly as you go by, then double your score because I guarantee the person you just passed will be able to think of nothing else for the next 72 hours.
At Glentress a few years ago with my then g/f, riding up the fireroad climb towards Buzzards Nest, both on our regular HT's, nothing special. Chatting away as we climbed, we passed a couple of guys in full lycra, carbon HT's, the works. "Morning" we said cheerily. One of them looked at us slightly disdainfully then said quickly "We've already done a lap of the Black", this obviously being his excuse as to why they was being passed.
Given that this was about 8am we doubted his statement and we saw them later arguing about where the trail went so they obviously hadn't done it before. We were more confused about why he cared so much about being overtaken…