almost always used in a sarcastic or unserious tone to demean another person's sometimes serious comment or message about something upsetting. similar to "i didn't ask", "go cry about it", "i ain't reading allat", or bluntly, "idgaf". it's supposed to imitate the common trombone sound effect heard in cartoons when something unfortunate happens to a character.
*@ig.user1* this isn't funny at all. others can get seriously hurt from people doing stufflike this, it's not too late to take this down.