The old story goes that a dude would fuck a knothole if given the chance, but, really guys, you need to be careful where you stick your dick. The penis is a somewhat fragile piece of equipment, and if you're not careful with it you'll impede your favorite pasttime by damaging it. So, take note of these places not to stick your dick:

5. Your Ex

This isn't necessarily about damaging the penis, exactly, but the emotions connected to it. You're ex is an ex for a reason; don't let the comfort of a known party to cloud your judgement by either making a booty call, or accepting a booty call, from someone that's a former sex partner. The fallout isn't worth it.

4. A spot of friction

A penis gets hard, sure, but the outside layer is soft and fragile. Most soaps don't provide a lot of lubrication, plastics are smooth but not really slippery, and humping anything covered in fabric is guaranteed to cause a rash. Even dry skin can be a bit of an irritation. Circumcised guys even moreso: there's less 'stretch' for you, which means the rubbing is going to leave a mark. Invest in some lube before you start rubbing against most materials. Make sure you use some real lube and choose your hump-targets properly.

3. Too basic or too acidic

Fucking some sort of fruit is a time-honored hobby of anybody with spare melons, but be careful which kind you partake in. If you're using something not designed as a sex lubricant, and it's significantly more acidic or basic than water, it's going to irritate your skin, and you're gonna have a bad time.

2. Anything too hard to break with your hands

The news loves a story about some guy who decides to fuck something made out of metal -- benches, machine nuts, weightlifting equipment, etc. -- and the aftermath in which a fire department needs to cut said item off the penis with the Jaws of Life. Even once a penis gets hard, it can engorge more during the excitement, causing it to get stuck, and once a penis gets stuck, the blood vessels are kinked closed so the blood can't get out and the penis can't go flaccid again...and now your dick is trapped. Make sure any place you stick your dick can stretch, unsnap, or be broken free without the help of twenty firemen.

1. Anyone who doesn't want it stuck there

It should go without saying, but some people turn into assholes when it comes to where they want to stick their dick. If the intended receptacle is another person, make sure they actually want that penis coming towards them. Like, actually wants it as much as you want to put it there. Imbalance in that amount of excitement is a sign you're not wanted there, and that's the last place your dick should be.