Looking for butt expansion source

So I was looking through TVTropes, went to their Breast Expansion page, and noticed something mentioned under the Misc folder.

http://tvtropes.org/pmwiki/pmwiki.php/Main/BreastExpansion

"Subverted by a birthday card of the late 90s; a flat-chested girl wishes on her birthday candles for cleavage. Her butt grows to immense proportions."

Does anyone have a source on this? I don't know why I'm so curious, but it's been driving me insane. I'm not even expecting anything good, I just really need to know what it's talking about for some reason. I can't find anything on google, I don't even know what to look for.