This movie's ending was shocking to so many viewers it became the prime example for people who prefer to not spoil the ending of a movie or book by knowing how it ends. Most people refer to this movie in terms of whether they knew the ending or not.
"Harry Potter 6 is the next Sixth Sense."
"La la la la ... I don't want to know the ending! My bitch-ass brother always Sixth-Senses me and I've been avoiding him until Sunday."
"Dude, don't pull a Sixth Sense on me -- I don't want any spoilers."
The sixth sense is probably a sense exclusive to one person, and one person only. All humans possess the other five senses, which are sight, hearing, smell, taste, and touch. But the sixth sense is whatever that person's special gift is, and is often a paranormal capability, such as seeing dead people.
"Seeing dead people, reading minds...what is YOUR sixth sense? What is mine? Well, I don't have one. -_- "