That when no one is around you can park the trailer first go perfectly. Yet if anyone is about you loose all ability and spend 47 hours going back and forward doing an move you have done, easily, a million times before??
It's the worst! One time I was reverse parking and asked my partner "is that man watching me park?" - he said no and the second I finished parking confessed he had in fact lied because he knows how much I hate it!
Also one time I did a good parking job, a guy in his van I parked in front of decided to compliment me on this and I just couldn't help but think he wouldn't have commented if I was a bloke (but that might be the cynical feminist in me overthinking it...)
ETA - realised you said trailer, I've never been let loose with one of those. Probably best for everyone