1) One who likes to perform the action of sticking one's finger up the anal cavity of another human being, usually being male,and/or ugly, as STM also denotes being a queer.
2) Can be used in conjunction with yayaya.
1) So, STM I hear you anally fingered that queer guy!?!? STM....YAYA YOUR NOT GAY!
"Smile To Myself" - When you're not actually laughing (or feel that LOL would be overkill), but the text joke did get a smile out of you (internal or external).