Lulu was a prostitute, but she didn't want her grandma to know. 
 
One day, the police raided the brothel and took all the girls outside and made them line up.
 
Suddenly, Lulu's grandma came by. 
 
Grandma asked, "Why are you standing in line here, dear?" 
 
Not willing to let her grandma know the truth, Lulu told her that the police were passing out free oranges and she was just lining up for some. 
 
"Why, that's awfully nice of them. I think I'll get some for myself," Grandma said, and she proceeded to the back of the line. 
 
A policeman was going down the line asking for information from all the prostitutes. When he got to grandma, he was bewildered and exclaimed, "Wow, still going at it at your age? How do you do it old girl?" 
 
Grandma replied, "Oh, it's easy, dear. I just take my dentures out, rip the skin back and suck em' dry." 
 
The policeman fainted.