A husband, tired of his wife asking him how she looks, buys her a full length mirror. This does little to help, as now she just stands in front of the mirror, looking at herself, asking him how she looks.

One day, fresh out of the shower, she is yet again in front of the mirror, now complaining that her tits are too small. Uncharacteristically, the husband comes up with a suggestion.
"If you want your tits to grow, then every day take a piece of toilet paper, and rub it between them for a few seconds."

Willing to try anything, the wife fetches a piece of toilet paper, and stands in front of the mirror, rubbing it between her tits.
"How long will this take?" she asks.

"They'll grow larger over a period of years," he replies.

The wife stops. "Why do you think rubbing a piece of toilet paper between my breasts every day will make them grow over the years?"

The husband shrugs. "Why not, it worked for your arse, didn't it?"