When you're under the delusion that two mask are better than one. This is not to be mistaken for double bagging or a two bagger. Double Masking is not for your protection but for the protection of others.
Kyle: You know that chick Emily?
Alan: Yeah, she's a total babe, the opposite of a two bagger.
Kyle: What I wouldn't do for a girl like that.
Alan: I know, even double masking is on the table.
When the man is about to reach his climax, he stands on an object above the girl and rains his cum down on her, like a pigeon does with its poop on unsuspecting new yorkers. He then proceeds to flap his wings and tries to fly away.
Pigeon masking: Yo dude, I totally pigeon masked your girlfriend last night...she'll be washing the jizz out of her hair for weeks!