Mythybusters proved that is only a problem in unusual and unlikely circumstances so any man that does that deserves to be labeled a sex offender. Their kind just goes around looking for reasons to take off our clothes. The AED excuse is not a valid one.
The AED instructions (written in the manual and spoken by the machine upon activation) almost always state to remove clothing. Non-professions would almost certainly be covered by a good samaritan law (heck, you're covered if you accidentally kill them, let alone expose them in public). Professionals who disregard the instructions given by the device might even be liable for malpractice. The instructions given by the device are approved by the FDA, and the device is only certified to be effective if used in accordance with instructions.
Sure, the bra might not cause sparks, but you're supposed to do things by the book. The AED is not programmed to argue with an operator - the instructions are streamlined for emergency use and if there is some reason the model might be less effective with a bra on the instructions will not say so - they're just written as if they will be followed.
It has been a long time since I saw that Mythbusters episode and I was not very familiar with AED operation at the time, but something that occurred to me subsequently is that they probably didn't test the diagnostics capability of the AED. If the presence of a wire near the sensors interferes with the diagnostics in the device it may make an incorrect treatment decision, either failing to shock somebody who should be shocked, or delivering a shock to somebody who should not receive one. Either is potentially a life-threatening error. It would not really be possible to test this without proper equipment/etc, since you need to simulate the heart/chest/skin/etc electrically to do it.
In any case, anybody reputable who would testify in court is going to say that the primary consideration should be to take any measure that will maximize the likelihood of saving the patient's life, and that is going to include removing clothing. Why take a chance over something as silly as modesty? If you show up in a hospital trauma OR the first thing they're going to do is chop every stitch of clothing off of you, and for good reason.