Anyone can do this, either:
a) Wear tight pants and have a decently big dick and fluff it up or get a complete erection.
b) Stuff an object into said tight pants and pass it off as your penis.
I will never understand why people fall for these "bulge" tricks.
On a side note; he's clearly not asleep and is purposely drooling to try and trick people into thinking he is so he doesn't look like a pervert and can "unwillingly" show off his erection and/or fake object. What a loser.