Clothes that are sewn askew
Short answer: If the side seam does not run straight down the side, the fabric was cut askew. It does not correct itself, and it gets worse after washing.
How to see it
Lay the garment flat on a table with front and back on top of each other. The side seams should lie straight and parallel. If one turns toward the stomach, there is a skew.
The difference between sewn askew and twisted
A tubular garment can twist after washing because the knit was tensioned unevenly. That is a different fault from a skewed cut, but the result looks the same. See bamboo t-shirts for men.
What you can do
It cannot be corrected. If the garment is new, exchange it. If it has been washed many times, it is wear and not a fault. See bamboo t-shirts for women and bamboo clothing for women.
Frequently asked questions
How much skew is acceptable
One to two centimetres across a whole side is within the normal range.
Can it be ironed out
No. Steam corrects a crease, not a skewed cut.
Does it happen more in cheap clothes
Often yes, because the layers are cut in taller stacks and shift.