Never by accident. Back in the day we would shotgun every time a joint was lit.
You take a hit, turn it around, then blow back to your partner.
View attachment 4502025
Another method involves a little more complexity than simply blowing smoke in someone’s face. In lieu of taking the hit from the blunt, you can invert the blunt to position the lit part in the center of your mouth (as in the picture above) and blow at an increasing intensity, while the other person catches the stream of smoke and sucks in until they have received an adequate hit. Although this may seem tricky at first, with a bit of practice it can be great fun delivering an amazing blast to the face. Personally, I recommend using your teeth or pursing your lips on the center of the blunt to avoid slipping and potentially burning the inside of your mouth. The one downside to this method is that the person giving the shotgun will not get much, if any, smoke, because they are dedicated to delivering it.
It was a lot of fun then. I could not imagine doing it today.