Use a sharpie to draw a skull and crossbones on one side; on the other, write DANGER.
When they ask you to hand over all personal electronics, point to it and say "that's dangerous".
If, subsequently, they want to know why you were carrying it ... it was so you could fry the USB port of your own laptop if you thought someone had snuck some hardware-level malware into it.
If you tell them NOT TO DO IT and they go ahead and do it, I find it hard to see how a court could convict you of wilfully damaging their forensic equipment.
(To the extent there's any social engineering involved, it simply relies on the tendency of police to ignore or discount unsolicited information from members of the public who are under suspicion.)
Note that they won't be sticking the device in a laptop or desktop PC; specialist forensic imaging machines are used by law enforcement to duplicate data storage devices and maintain a legal chain of evidence. Oops.
If the TSA or foreign equivalent border security want to scan your devices, it's their look-out.