There is no way to be 100% certain of your sexual partner's health. And many guys are walking around with HIV and other diseases without even knowing it. It's a fact that it takes 3 months, and up to 6 months, for HIV to even show up in the lab work (just ask your doctor). Therefore, you may saythat you're negative, and even believe that, but in fact, may be positive.
And, many guys DO lie. Sex is as strong a desire as the desire to eat, and many guys will lie to have sex. Why? The stigma that many in our gay community have put on HIV+ guys. Some of the nicest guys I know are HIV+, btw.
In my opinion, it's up to you to keep yourself safe. In 2001 it's foolhardy to play unsafe and say "you must be HIV negative too"...You'd actually trust a stranger with your life?
My doctors says that if you assume everyoneis HIV positive, then you'll practice absolute safe sex.
In my opinion, you assume all risks when not playing safe.

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5'11", 160lbs, 31" waist, 41yo. Short hair, clean shaven/clean cut appearance. Exhibitionism, nudity, 100% bottom, SAFER SEX ONLY (condoms)! Love "servicing" straight/bi guys, and love rimming shaved, hot holes.