When I get a new article of clothing, I always use a pair of sharp sewing scissors to cut off all the extra threads hanging from seams and buttonholes.
Also, on many new garments, there is a piece of thread inside the buttonhole that didn't get snipped. If you leave it there, it's hard to push the button through the buttonhole. Or even worse, that thread can get pulled, and end up snagging the fabric! So I check all buttonholes for extra threads.