It's easy to assemble many bikes with the fork backwards. The bikes come with the stem uninstalled. The fork (threaded) is already mounted to the frame but is turned around backwards so the bike fits into as small a box as possible. Most of the walmart bikes have straight forks and with no curve at the end. You have to look carefully to see which way is forward. When the bike is assembled, the fork must be turned 180 degrees before the stem is inserted. It's easy to forget to turn the fork. Many of the bikes have a sticker with an arrow pointing forward, but it's easy to miss that as well if you are in a hurry.

The small kids bikes are the easiest to do incorrectly. The forks are so short that the rake is not very apparent regardless of orientation.