"A long time ago, my (then current) gf did exactly that when both of us were 'in between jobs'... One day I came back early from jobhunting and found them in the living room. She on all fours, he mounting her from behind, fucking her doggy style. When he noticed me, he grinned, sped up a little and nutted deep in her pussy. After he left, we had a big fight, followed by the best make up sex ever... Sloppy seconds never felt so good."