If you are struggling with your own comfort, my first suggestion is to make the conversation as non-personal as possible You will have an easier time talking to your teen about condoms and your teen is going to have an easier time listening if you are speaking in general terms.
Second, focus on the health aspect and impart information. If your teen isn't comfortable or ready to talk about this, save the need for dialogue for a different day. Below is an example of what I mean. Please take this concept and customize it for your own situation. I will use the name Tom, but in choosing a son, I'd like to add that this conversation is just as important for daughters, as females are often on the receiving end of guys' excuses about why they don't need condoms. I also recommend making notes, or at least have bullet points, so you are sure to cover all of the points you want to make.
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Tom, I read something really surprising today and I want to share the information with you. I'd just like you to hear me out. I am open to answering your questions if you have any, but mostly, I'd just like you to hear what I have to say. I am sure that you have heard it is important to use a condom.
Then you would discuss the statisics I provided. For instance:
I was really surprised to learn that most teens think that you can visually tell if someone has a STI. This is absolutely not the case. Further, one out of every four sexually active teens currently has a STI, and one in two sexually active youth will contract a STI by age 25.
When I was young, most STIs could be treated with antibiotics, this is no longer always the case. Your generation is going to have to be very aware condoms and how to properly use them more than ever before.
Now, a recent international study by the Kinsey Institute found that 80% of condom users are improperly using condoms. I didn't even know that was possible. But it is pretty important to know, because if a condom user isn't wearing a condom properly it defeats the purpose.
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The study also stated that the most common errors include putting on the condom too late and taking the condom off too soon, not leaving space at the tip, and using a non-compatible lubricant. I also learned that many of the errors are related to wearing the wrong size condom. I never knew there were three different sizes of condoms; I always thought one-size-fits all.