live one

noun3

1. •
   (informal) A person, thing, or situation which is particularly interesting, noteworthy, or urgent.

   • "We got a live one here," he said as he speeds up in pursuit of a car. — 2007
2. •
   (informal) Someone who is eccentric, nonconformist, or otherwise peculiar.

   • They've got a live one in the crowd, he's scary, he looks dangerous, demon possessed, he doesn't know who he is, he speaks in strange voices. — 1997
3. •
   (informal) Someone who is easily fooled, victimized, or ridiculed.