The penis isn't a terribly delicate organ – but it is made of skin and flesh, after all. In fact, the skin is much thinner on the penis than, say, on your hand or arm, so it can actually get damaged pretty easily.
1. Never insert your penis anywhere there's a chance it could get stuck. If it gets stuck just a little it will swell, and then it'll be stuck for good. A friend who's an emergency-room physician once had to use a diamond-cutting saw to remove a metal wheel bearing from a man's penis. You do not want to be that man! Few things could be more embarrassing than walking into an ER with an injury caused by an irresponsible sex act. Before you try to have sex with a bottle, think for a minute about what that would be like.
2. Don't try to enlarge your penis using any non-medical method. A larger penis is something most guys would really like, and some do anything to try to get it. That's why there are so many "penis-enlarging" devices being sold in the backs of magazines by unscrupulous people out to make a buck. But these devices can be harmful. They can unnaturally stretch your tissues, and the ones that use a vacuum pump can be really bad for the blood vessels of your penis, which are responsible for erection. Even if these devices worked, what would you rather have: a natural penis that works, or a slightly larger one that will never get erect again? Don't believe the hype – your penis is fine the way it is, and treat it well.
3. Don't masturbate with a vacuum cleaner. Many guys, in an attempt to simulate the suction action of oral sex, play around with a vacuum cleaner hose. For the same reasons as #2, this is a bad idea. Anything that creates more suction than a human mouth can injure you.