The smile you have after your friend says something funny or makes you laugh and you leave, making a fool of yourself as you walking around with big smile on your face. It is especially awkward if you look at someone with an after smile because they think you are smiling at them, but you are just looking with an after smile.
Person 1: <Insert Joke here>
Person 2: hahahahahhahhaa
(Person 2 turns around and walks away with an after smile)
(Two Strangers walk by Person 2)
(Person 2 looks at Stranger 1 with after smile)
Stranger 1: Did you see that creepy guy smile at me!
Stranger 2: Yeah! It was really creepy!