The most well known is probably 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0 which was a decryption key for Blu Ray discs, allowing you to get around DRM technology.
So any criminal activity, not just CP, would be a good reason to not want to be searched at the border.
It's probably worth noting that since the search is still _allowed_, information can still be divulged from devices and then used as the basis for a parallel investigation (I believe), provided that information isn't used as evidence. So it doesn't sound like much is practically different, so much as technically legally different - slightly more hoops must be jumped through to convict based on arbitrary device searches, is all.
Citizens, I suspect not. But unclear for noncitizens who don't have a defined constitutional right to enter. (In the past noncitizens who declined searches could risk being denied entry)
I wouldn't lecture them on the law - a border (or the side of the road) isn't the place to debate what is illegal - that just gives them an excuse to claim they felt threatened.
I'd just assert my right to remain silent, let them seize the phone, restore from backups when I buy a new one, and contact a civil society organization when I get back out.
(And as a practical matter the phone is backed up and I am privileged enough to be able to buy a new one if needed)
> We use the term child sexual abuse to reflect the gravity of the images and videos we deal with. Child pornography, child porn and kiddie porn are not acceptable descriptions. A child cannot consent to their own abuse.
A child taking their own sexual photos of themselves, with no other person involved, would still be child porn, but not child sexual abuse.
Eventually we will get to a state where searches are not done “because reasons”.