Some eye candy
 

Nice black briefs, fit slim body, good first attempt, I'd love to see more.
Are they Lycra swim briefs or cotton underwear briefs, if Lycra swim briefs get them wet in the shower for full shiny clingy effect.
Clean the mirror before shooting for a better image and try to position the phone in a less dominant position, perhaps using the camera the same side as the phone screen (and no mirror) or using the countdown on the camera (sing Nellie the Elephant as the camera counts down to be relaxed when the shutter clicks).

Wearing only the briers would be the biggest improvement.

This was just a quick on the cuff cell snap, not a posed shot. Photography critique kinda like telling Scorsese that because he took a bathroom selfie like this he needs photography lessons. Not everything is or needs to be a production. :)

To answer question these are Lycra briefs.

I will make sure I post one in the speedo shirtless dripping wet with a nice bulge. ;)