Having a boxy frame is great when you're wearing something that's heavily patterned. Stripes look amazing when they're allowed to be completely straight. The same goes for plaid and checkered patterns.
The easiest way to achieve this is to wear a shirt over a thin sweater. The extra fabric bunching up under your shirt forced you to realign the two garmets until the outer most layer looks straight. The texture of the two shirts rubbing together will force the shirt to stay in place.
It works sort of like filling in an empty place. A bag with nothing in it will dimple, but once you start filling it up, it becomes smooth. Doing this by using layers is the most sensible way, and it also provide a lot of extra warmth.
I highly recommend this to anyone whose a fan of box dresses. Since it can be used on any top, it's the easiest way to create shirt dresses. All you need is an over sized shirt and a sweater that doesn't itch. Big button ups fro the men's section works especially well with this, and adds some variety using "more masculine" patterns. A chunky belt will make it look ore like something you grabbed off the rack, especially if you can find some matching shoes.