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 end 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.