I wore a sports bra for my grope. The TSO didn't try to get in between my breasts. She just dragged her hand across the top of my breasts and again below them.

However, procedures apparently vary widely.

If this were really about security and not just humiliating theater, you'd think they'd want to check in the space behind the wall of elastic on my sports bra. But I had the impression that the pat-down was more a punishment for opting out than an effective security check.

One thing to remember as they grope you is that they look a thousand times more ridiculous doing the procedure than you do simply standing there.