[1231232131231]

Most definitely not. If you're jailbroken, you can set an automation to delete the /var/ folder and soft brick your phone (until you re-flash it with iTunes).

You could also set up your passcode so it clears your phone after a few wrong attempts, then purposely enter the wrong passcode.

At best, physically crush your phone in a way that destroys the logic board.

[pc86]

I'm sure you could engineer a case that pierces the right parts of the phone such that it is effectively a [self-?]destruct button.

The biggest issue with this of course is that if you have a legitimate threat profile that requires you to be able to quickly destroy your iPhone, you're not going to have an iPhone in the first place.

[pavel_lishin]

Or one of those USB-killers that sends enough current through the USB port to burn things out.