I love this thread. Funny thing as a player myself (sort of) I do this all the time, but of course I'm always right.
My best one, I had a County Cup match last season which the home team were losing, and the net kept coming away from the post, which (of course) led to them questioning whether one of the goals actually did go in.
One of the parents watching, who was "a qualified ref" told me that I had to abandon the game as the nets weren't attached properly and couldn't be fixed, and you "have to have nets in all matches". I told him nets were not required in the LOTG and therefore he was wrong and we could remove them at half time if agreed, he went mental telling me I was utterly wrong and made a massive issue which ended up with the manager and all of the other parents coming on the pitch and telling me their 'expert' must be right. I always keep the LOTG book in my bag, so I pulled it out and showed them the Law.
Obviously I was aware there was nothing additional in the competition rules to overrule this.
Cue smug face.