I did it once. Not the 'What's a thigh gap? Oh, this little thing that I surely wouldn't put on Twitter?! But it's just the way I am!' bollocks, the putting a g-string on the wrong way.
I had to put paper pants on at a spa for a massage. I thought the paper bit provided overall coverage if I put the widest part of the triangle on my buttocks, and it was only when I lay down and realised I had an obscene front wedgy that I realised. I just had enough time to climb down, put them on straight and get back up before the masseuse came back. It's the last time I had a massage and the last time I wore a g-string, paper or otherwise.