Tone, like from the Freakout's definitions

lol

A qualifier used to diffuse tension at the end of a particularly serious statement. The user of this qualifier usually anticipates a negative reaction (the nature of which is either anger or awkwardness) from the listener, and thus hopes that adding the word "lol" will convey a tone of facetiousness, which is often not discernible in netspeak.

Johnson: Hey Timothy, last night I shat in your mother's vagina and farted in her mouth, after which I proceeded to masturbate on her face and urinate all over her body lol.
Timothy: Haha, oh Johnson, you never fail to amuse me.
Johnson: I wasn't kidding, lol.

by Tone, like from the Freakout December 15, 2008