That you're not crazy in a crazy world is crazy.

Correct use of a condom means

Using the right size, because if it's too big it can slide off or leak and if it's too small it can break or come off. Condoms usually come in 5 sizes, I'm sure you could find others outside of that as well but in ten years of sex work I found they covered everyone

Using lube, even if you think you don't need it. With the exception of oral sex, condoms should always be used with lube, 100% of the time. Most important lube should be applied to the outside but a drop in the tip of the condom before putting it in is also a good idea

Being mindful that latex is prone to wearing out, being damaged by heat etc. Condoms should be kept somewhere cool, not folded in wallets or sat on in back pockets and should be changed between activities and after about 15 minutes of any vigorous activity. Ask me how I know (a condom snapped on my leg when a client was pulling out, because I didn't change it when I should have)

The penetrative partner should hold the base of the condom when they pull out, and should do so immediately after they ejaculate so the condom doesn't leak or come off as the penis gets flaccid

Bonus: a lot of people think hand stuff can't transmit STIs. Wrong! If you give your partner a handjob and then touch yourself you can get HPV, herpes (low risk), and infections like chlamydia and gonorrhea

This isn't meant to be stressful, and the most common STIs are the most treatable - and often curable - but getting gonorrhea in your eyes after a facial still extremely sucks and yet no one talks about the fact that any mucous membrane can be effected, not just your genitals (yes this includes your mouth and throat)