I'm not sure when the last time I've said, "Now, I've seen everything" to myself was but it was probably followed by somebody asking me if I've seen whatever outlandish thing comes to their mind.
For instance, if somebody told me they've seen everything, I'd ask if they've seen a guy dressed as Spider-Man climb a building.
But in case you haven't guessed by this point, the reason why I have to struggle to remember claiming to see everything is that I've long since realized that we never really run out of new sights in this world.
After all, I'd find it a little hard to believe if you told me you've seen literally everything on this list.