Mhm: Self-explanatory
Mmh- Not a misspelling of "Mhm". Either: A slightly irritated, exasperated, or tired response to something /or/ An equivalent of "I see" with slightly more interest than "Ah", depending on the conversation at hand.
Ah.- Equivalent of "I see", sometimes dry depending on tone.
OIC- Oh I See, less serious than "Ah."
OuO, or sometimes O3O or rarely OvvO- The emoticon with a million uses. Usually used when one seems necessary, the conversation is not serious, and no other suitable emoticon can be found.
Yey- "Yay" misspelled on purpose for no reason.
B|- Imagine somebody in Men In Black shades looking down on you with their arms crossed.
Myrrh- Irritated, usually forced response (usually forced, disdainful agreement) to something.
Ggh- Very irritated response to something