Just to help anyone reading the thread:
IMHO - In My Humble Opinion
IANAL - I Am Not A Lawyer (Mostly used in threads about legal issues)
LOL - Laughing Out Loud (Meant to used for something funny when you laughed out load at it, from what I've seen it's used in many places where that is not the case thus making it useless)
OP - Operator (I've used it as part of "topic OP", referring to the person who started a topic)
On IRT, I haven't seen that one before.
As for things like OP or even OS you are right I have used them in some topics.
I usually try to write out what something means if I think it won't be understood but sometimes I miss something.
You are right that some faces can come in handy.
I was just saying for the faces used in an image can be interpreted in different ways as they aren't all known.
Like the image Scott posted above, does it mean just happy or super happy.
On the posts with "topic op", I mainly just used it to avoid using he/she as I have no idea which the topic op is.