From a corner kick would be an obvious one because doesn't it count as the goal line and the fact technically the ball can't be played forward?
Not really, I thought about that too, but it could be that the ball is placed as far to the left of the "D" as possible:
Today, the ball is barely in the "D" so you could get another 40cm to the left in that picture.....
If all the defenders are lined up on the 6yrd box marking up, you could have one player right on the byline on the edge of the 18yrd box and the ball played diagonally forward to him.
The worrying thing is this is a perfectly legal move, yet I bet 9 out 10 times it would be flagged offside, and if it wasnt, and led to a goal, you would have all the nonsense we are having now, by people who dont know the rules.