It's true. Big pants are best. Think about all the times you've sat a little off and had a wedge of your trousers or skirt position itself in your ass. There's a reason wedgies are still the schoolboy's prank of choice - they're bloody uncomfortable. So why on earth pay good money for the same experience? Especially when in most instances the scrap of fabric that makes up a thong costs about the same as its big knicker sister.
And she's right about one thing. Most blokes don't really care what your knickers look like, they're just happy to have got to that stage with you!