Reassurance Smiley
When someone says something that may otherwise be mistaken as serious, but follows it with a smiley that helps reduce the tension and lets the second person know it was a joke.
Dude 1: Your mothers a filthy whore
Dude 1: :P (reassurance smiley)
Dude 2: lol
Dude 1: :P (reassurance smiley)
Dude 2: lol