H&M ain't dumb. You don't buy your own underwear, gentlemen. Other people buy it for you: your mother, your girlfriend, your boyfriend, your wife, or perhaps your manservant. All male underwear buyers therefore by definition love David Beckham, and thus he's a logical pick for underwear ads. (Your manservant is British, and therefore loves Beckham for soccer reasons.)
Still, this is a man in his drawers on your screen, which for the ladies and man-loving dudes is great, and for straight dudes is a problem because a.) he's attractive and thin, which by the numbers you probably aren't, and b.) because all you insecure guys are like, "LOL, I don't need to see this because I'm not gay, and this hot dude on screen is totally unnecessary, what with his lithe figure and impeccably cut figure."
This is probably what you were thinking, or should be thinking to cope.
"Whatever, dude. I got better pecs than that."
[/flexes man boobs]