If HIV isn't in the saliva, then why is the test an oral swab? The oral swab isn't gathering saliva or HIV. It's looking for HIV antibodies in the gum tissue. This is why you don't want to go scrubbing about.
Do bug chasers really exist? Yes, they do. People hoping to contract HIV do so for many reasons, some of which include: 1. having experienced the horrific AIDS related deaths of their friends in the 80s, they want to die in the same way. 2. as a way to commit suicide somewhat passively. 3. It's a way of sharing something with another person. If they're unable to have offspring together, baby kind, then they parent HIV. There are underground networks for these kinds of relationships where they use their own lingo, like the golden hand of Midas, or gift-giving. 4. Some feel that contracting HIV is inevitable. They want to control when and how it happens. If you'd like to know more about it, there's a documentary on this very thing called The Gift.
So, Lindsey, my girlfriend has this cut in her mouth, she's bleeding, and if I kiss her, can she possibly give me HIV? Get tested before you become intimate and use sex shields to protect yourselves. Remember, the mouth is not a super hospitable environment for HIV. Do you need to kiss her bloody mouth? 
What is the difference between HIV and AIDS? Oooh, I answered this question in an interview with Hank Green on SciShow. There's a chinchilla.
Is HIV in urine? No. Feces? No. Tears? No. Sweat? No. Saliva? No. Boogers? No. Pre-cum? Yes, totally in precum. 
Why is having another STD a risk factor? In a happy, healthy vagina, the immune system is hanging out in the submucosa, the layer below the mucus membrane in the vaginal walls. If chlamydia enters your body, then the immune system will come out to fight. You know it doesn't win, because you have to take antibiotics and your partners have to take antibiotics, but it tries. So, during one of these high alert times when your immune system has been traumatized by another sexually transmitted infection, it's right there eon the surface and- woop- HIV has immediate access to its host. Remember, it needs the immune system calls in order to survive, another reason to get yourself tested. Other things can bring the immune system cells to the surface in the vagina, vulva, urethra, the penis, anus, rectum. 
I imagine that some of you have more and more questions. I've put links to the answers you may be looking for in the doobly-doo. Stay curious and get tested.