Here are some of my standard lines I use and exactly when I use them:

“That was good. What there was of it.”
Usually said right after a gut-splitting meal. Why? My mom would invite a friend over to our house for our massive family dinners when I was a kid. She would always be amazed at the size of the spread for a family of seven and would utter that phrase ironically as she shoved herself away from the table with a groan.

“Did you look under the bed?”
Always said after “We’ve lost XXX” in terms of a death in the family. When the last woman I ever dated (Donna C) had her parents die within months of each other, her best friend at the time came over to her house unaware that they had “just lost Donna’s Dad.” Without missing a beat, that is what he replied.

“We shall have fog by tea time.”
Rumour has it that the Public Relations minders for the Queen Mum told her to say this when she was faced with a situation she didn’t really understand or could be potentially damaging socially, like meeting militant dykes at a reception or introduced to a murder or something. It does work, I find. Just this evening someone loudly asked SharkBoy how his dad was doing. Sheepishly he answered, “Uh. He died in June.” Uncomfortably long silence. I uttered that line and the conversation was back on track!