How bad is redlining my 2006 Honda Civic?

It's actually not that bad if your hitting around 6800Rpm's. Your just making use of the i-VTEC. But that being said, you will burn through oil faster, and you'll get less gas mileage. You will put more wear on engine parts, but your not really going to damage it, just be sure to keep up with your maintenance. Don't worry about it too much though, you've got 40k miles and you've only done it about 50 times, so thats probably actually good for the car that its seeing higher revvs once in a while. Btw the oddness you feel in the way you respond is simply because the car has a small 4 cyl engine, i have the 08 model, same engine and all, and i notice that too. If you have the AC on when you push down on the pedal hard, the car will take even longer to rev up, or it simply won't get that high at all. So its good to make sure your AC isn't on if you really need that extra juice. I have to hit 6800rpm's to get up this very very steep highway onramp in my town, and that's at least twice a day, no problems.