Example:
J ayden Trickster looks around eying the crowd on the courtyar d
A metapose is when an otherwise ordinary information is beefed up with information no other character in the scene could respond to by valid RP means.
J ayden Trickster looks around eying the crowd on the courtyard in order to check if theres some angels around whose legs she could hum p
Usually this isn´t a big problem and in certain RPs oftenly used to make the story that´s being told more enjoyable for the participants. In most cases you may consider metaposes as an acceptable part of narrative roleplays. However, as you can see there is absolutely no way an angel could respond to that pose, although now already aware of a danger. The only information that one could respond to is that Jayden is looking around.
Metaposes sometimes even encourage other players to metapose in response, which leads to a rahter silly mind-reading-"RP". Metaposing is often used as a means of passive-aggressively getting in a "last word" without having to deal with any IC consequences. This sort of thing is awfully frustrating to deal with and must be avoided:
J ayden Trickster approaches Lisa, grinning predatorily. The look in her eyes is somehow indicating she may have some evil plans in mind. Perhaps she is once more out to seek some angel whose leg she could hump. "Hello Lisa "
L isa Winchester glances back frowning before she suddenly turns around and takes flight, running away from that ugly lycan, believing all her family members are assholes and full of shit "
You see how Jayden is approaching Lisa using a metapose that may not be very clever or "right", but still is acceptable to give the roleplay some flavour and let others learn about her background and her possible intentions. Sometimes you may need this to kick off things or keep things going.
However, you can see the big difference in Lisa's metapose-response. It´s very frustrating for Jayden now to find her character now coming under the fire of IC insults that she cannot respond to. If you feel the need to insult a character in a post, then do it in such a fashion that gives the other character a chance to respond to the insult accordingly; whether the insult be verbal, or expressed via a dirty look or unpleasant facial expression.
Passive Aggressive attacks and insults worked into a pose are not only extremely poor RP Etiquette, but they are a quick way to finding yourself lacking people willing to RP with you.
DON'T DO IT!