I just had a look at my list of Peers in Core and seen that there is 1 banned peer, what is that all about? never seen it before.
Bitcoin Core automatically bans peers that it sees are misbehaving. If a peer connected to it misbehaves, it disconnects it and blocks it from connecting for 24 hours.
As for what misbehaving means, I'm not quite sure. I am fairly certain it has something to do with the number of transactions and blocks it is sending and whether those transactions and blocks are valid.