Lozenge Shaped Shampoo Bottle
Not lozenge-sized, mind you, although that would be a terrible idea as well.
Why is it Terrible?
Because it's round on both ends. You couldn't stand it up in the shower and the shampoo would be forever settling on one side of the bottle. Extra terrible points awarded if each end of the bottle was different (shampoo conditioner combo, for example). You couldn't use one without having the other one run to the back of the bottle.
If you had a weebil-style bottle that was weighted on the bottom by product and could never be knocked over then that could be cool. But it wouldn't work when it was full; it would just topple. So it would be full-on weebil action for like... 10% of the bottle's lifespan and the rest would be in-shower frustration hour.