The first step in dealing with any threat is to acknowledge it. If someone says "It's been a long day and I'm tired" they're saying double check my work, I may be more prone to making errors. My judgement may even be impaired. Don't even think about practicing that manual thrust, raw data ILS and let's not do 340kts to 5100 feet, even if we're offered it. CRM is all about acknowledging that we are human and make mistakes and letting the other guy know that, at the moment, we are more human than normal.
I certainly hope that mentioning "I'm tired tonight, watch me" doesn't invoke any negative conotation like "well weren't you rested?" etc.