One of these.
A little boy was playing in his sandbox when the little girl next door came up and asked if she could play, too. He said, "okay."
Shortly he began bragging, "I have a big fire engine."
The girl responded, "So, I have a fire engine too. See!"
Only slightly put off he expressed, "I have a toy tank!"
She looked at it and quietly reached behind the sand box and pulled out a toy M1 Tank and said, "I have one, too."
The young boy almost in tears dropped his pants and says, "I have a penis!"
The little girl looked down her pants and burst into tears and ran home crying all the way.
The next day the lad is playing in his sand box when the little girl approaches. He says, "are you back for more? I told you I have a penis and you don't!"
"Well," said the little girl, "my mom told me not to worry about it. She said I have one of these... and as long as I have one of these, I can have as many of those as I want!"