I changed all 6 of my spark plugs during work...
I was on the last one, had the new one in the hole hand tightened and was going to pick up the torque wrench to torque it down to spec when the boss walked out.
I saw him before he saw me, so I grabbed all my tools, put them in my car and walked around with my drink pretending to stare at my engine bay.
(I don't think he really would have cared if he saw me/realized what I was doing, but image is everything so I try not to appear like a slacker at work even though I am. (That's how I've gotten away with being a slacker for so long and not getting fired.)
I can't tell much of a difference with the new spark plugs, but some of the old ones were rusted to hell where there threads are, which I'm sure didn't let the heat escape from the engine as quickly as it should have.