This guy is really into blow-up dolls and phones his mail-order supplier and says, "I want something absolutely realistic..!!"

The supplier says, "I have just the thing.  'Life-like Tina.'  So realistic you can't tell the difference..!!"

The guy orders one.   Meanwhile, the supplier is looking at the box and cannot believe how realistic 'Life-like Tina' looks.  So he decides to blow it up.  Once inflated he gets really turned on and thinks, "What the heck..!!" and has sex with the doll.   Then, after washing it up, he neatly packages it and sends it out to the guy.

A month later the guy calls up, "You know that 'Life-like Tina' blow-up doll you sent me..??   I cannot tell you how happy I am."

The supplier says, "That's great..!!"

The guy relates, "Yeah, it's a totally believable experience."

The supplier replies, "Realistic then..??"

The guy says, "So realistic......I got syphilis..!!"