Meh, to like and hate something at the same time. Its like you don't like the idea, but another person does. They ask you for your opinion, and you don't to be rude so you say "Meh".
When someone has no good comebacks and ultimately submits to whatever they've been attacked with, as denying what the other said would be a blatant lie
"Man you're really gay, you know that? You make so many gay jokes I wouldn't be surprised if you sucked Tyson's dick."
"Meh."