Is a design crooked, off center, too low, too high or rotated right or left? If you are asking about it, probably it is a reject. If you let something go through and the customer gets a ruler out, you are done for. Shirts are made by real live humans and printing (and loading) is done by real live humans and the combination means there is no perfection involved. So, if you allow a borderline print without saying something and then if it comes to the attention of the customer?  They are usually going to look at that shirt very closely and then there is a good chance they will start examining all the shirts. Shirt printing cannot usually withstand that type of scrutiny. In my shop we say, “don’t let them get their rulers out.” If they get their rulers out, you are normally done for.