Serial.println("I am treacherous!!!");
Well I am using a Mega, but can easily test it on any board you want.
Ok not on "any" board... On a wide variety of boards? Is that better, AWOL?
I thought that had been fixed ages ago.
Not for the fake/chinese Arduino's
At this point, the problem may or may not be the compiler.
This was a "feature" of the old Mega bootloader. Arduino came to their senses and removed it quite a while ago but old boards or maybe some clones will still have the old bootloader. You can fix it by doing a Tools > Burn Bootloader using any recent version of the Arduino IDE.Fun fact: if you have verbose output during upload turned on you'll see it prints "Bootloader Huh?" over and over again.
If the problem is uploading to a Mega then the extremely generous people of this forum have already given you the answer despite your failure to describe the problem.