"Um...try to fit something on that works at least somewhat better," you suggested.
Your sister grumbled and suddenly the walls started to close in faster on you. "Oh god," you began. The walls finally pushed against you and you felt the urge to cum. It felt so good having her flesh cover your body and cock.
"I'm...gonna cum..." you moaned.

Your sister was breathing hard and shaking like crazy. She had just tried on a tight bra that was going to pop in a few seconds. As soon as you ejaculated, your sister moaned and the bra popped off along with a leaking lactation splurt. "Aah!" she screamed.

When the bra was gone, her breasts relaxed and you felt the pressure no more, it felt great though. "Sis...that was amazing," you moaned.
"I...I guess I should keep one on then if you like it so much..." she blushed.

You realized your mistake. You knew that it felt amazing and very pleasurable but you weren't sure if you could last that long.