I have a penis and breasts. What should I tell the TSA agent to prevent them from touching me?
There's no 100% answer that will always work. Between the 2 I'd say it may be in your best interest to explain your situation and ask to be scanned as male ... because the machine knows men can also have breast cause it happens with overweight men so MAYBE it wont alarm there. For women ... anything that draws too much attention to the groan area for that machine, be it fat or fabric, can set it off (which is why some older female TSOs will ask women to take a wider stance than they should if they're overweight or got big thighs. They're not supposed to do that but many Old People don't give a fuck and make up their own rules).
The machines are not 100% accurate or even consistent in it's own rulings so no one really knows fully what sets each off. You can scan a man as a woman and have them get a clear if the machine doesn't feel like what's in the groan area is big enough for example.
The over all BEST option to not be touched at the airport is to sign up for precheck. You're basically telling the Gov it's ok to do a background check on you and when you sign up It's not a guarantee that you will always get pre-check ... and even if you do get it the metal detector you walk through is set up to randomly select people for additional screening which
can range from testing someone's hands to sending them to the body scanner to just checking their electronics. But with precheck you go through the metal detector.
Or, if you have a cat or dog, bring them with you. You will be asked to go through the metal detector with your animal regardless of if you're precheck or not. They will simply have to test your hands if you're not precheck.
Or, if you have or are just traveling with kids 12yo or younger just say that they're yours. Parents go through the metal detector with the kids, they're not separated unless there's a reason.
But yeah, under normal circumstances I'd say just explain your situation to them and ask to be scanned as male. If the TSOs have any common sense between them they will try the male button if ASKED and let the female clear any chest alarm if they do alarm as it's much easier for them then getting low and doing a groan pat down. The groan is the big deal for them, everyone wants to avoid a groan pat down.
In 2018 O'Hare had 83,339,186 passengers. Trans people are roughly 1% of the population. Doing some math, that works out to 2,283 trans people going through O'Hare per day. Now, we could say that half are arrivals and so don't go through security, and that trans people (being statistically poorer than cis people) take fewer flights. There are still going to be at least 500 trans people going through TSA scanners at O'Hare per day.
Ohare is a huge airport and TSOs have to do a lot of different things. There's only 2 positions where you are asked to pat someone down, Body Scanner and Bag check (Bag check if someone ops out of the body scanner. If anyone's wondering why it may take forever to get someone to pat them down once they op out it's most likely because there's just no one free at the time).
So yeah, I may see a trans person ... when I'm at TDC, checking their boarding pass. Or I might see one in line ... when I'm doing DO or on X-Ray or at the mag.
When I was at the scanner I've noticed most trans women op out of the scanner in favor of just getting a pat down so as to just avoid the confusion.
I worked for the TSA at Ohare for over 2 years and only had to pat down 1 trans man that I can remember ( a teen with chest bindings that alarmed. Once they said bindings I realized what was going on, asked if they were ok with me doing the pat down, patted only enough to feel that "yup, that's bindings and breast" and sent him on his way).
A lot of this swims in gray for people because they're not exactly common. Plus they train men and women to do pat downs with out any consideration for cases like this. As a man I know what to feel for in a male groan pat down ... I've SEEN females do breast pat downs but that's not how you check a man's chest so I was never trained for that there for in the example above I just checked him the normal way as a judgement call cause that's what I know. Same goes for women which is part of why I've seen some few female TSOs who won't pat down a trans woman's goarn and instead ask for a lead or STSO to take care of them (they're not trained on how to clear a penis. Same thing applies to getting adults with diapers, if you don't feel like you can clear this area you bump it up to someone who gets paid more than you to handle)
What's far more common is ending up in situations where you have to make a call on someones gender when they don't clearly look male or female. There was new training about pronouns late last year because this is still something people need to learn about.