WARNING: The following is a joke, and is fully intended to be a joke. Do not take this seriously, nor follow these instructions.

Step 1) Make a pose that suggests that you are thinking, otherwise known as the "constipated face". Nothing gets the brain whirring than a good bit of mind-thinking.
Step 2) Get a knife from the kitchen. No, not a butter knife. That's right, the very sharp one. The sharper the better.
Step 3) Grab your flaccid penis in an OK grip under the glans and stretch it out slightly. You may want to warm it up first to avoid injury.
Step 4) Position the knife at the base at your penis and push down. You should feel a painful sensation; don't worry, this is normal. Continue pressing down.
Step 5) By this point, you should've cut your penis off. Hopefully the knife you used was quite sharp, otherwise you'll have to hack it off, and that can get quite painful.

See that stump you now have instead of a penis? Some guys are that long. Some guys are shorter! Be proud that you've got that much, and if the girl really isn't digging it, well, you've got a tongue, haven't you?

Step 6) To avoid infection, it is best to go to the hospital. You *can* sterilize the wound by spraying it with some alcohol rub, though this may make it sting like an absolute naughty word. But you have just sliced your penis off, so this might be right down your alley.
Step 7) Throw your penis into a trash can. A cute little beetle or mouse may make a home or at least make a meal out of it.
Step 8) ???
Step 9) Success!