I wouldn't be so sure. We know that there are plenty of bots out there constantly adding more and more private keys and addresses to their databases of cracked brain wallets, just waiting for coins to steal. Some fairly unlikely words and phrases have not only been turned in to brainwallets but have subsequently been cracked. For example:

Song lyrics - "voulezvouscoucheravecmoicesoir" - 13Rq3HxwJwHzcGK8TQE4MnK9CezazLG55t
Book quotes - "Down the Rabbit-Hole" - 1PYgfSouGGDkrMfLs6AYmwDqMLiVrCLfeS
Movie quotes - "Zed's dead baby. Zed's dead." - 12dyYjCxWzSJg7p8mpS3t7PhsL7Btb2rPB
Internet quotes - "correct horse battery staple" - 1JwSSubhmg6iPtRjtyqhUYYH7bZg3Lfy1T
Religious quotes - "gate gate paragate parasamgate bodhi svaha" - 1N8gLjZEhRxLRRjg8ymS6Zez8KVegEKtb1
Non English phrases - "que me lleve la muerte" - 1K9xaDfABruMHrvWtJ3DWPu1q3XTr5wxUS

And these are just the ones which are in the public domain. It is certain that there are bots out there with millions more similar examples which we don't know about. You should assume that if a phrase or sentence appears somewhere online, then at some point some bot will check if it is a brainwallet.