"The international date line is the line between happiness and sorrow. On that side, You'll be home tonight. On that side, home tomorrow."
- —
Barney Stinson, Bedtime Stories
The International Date Line is one of Barney's theories.
Its basically a globe that half of it is red with the title "Not a date" and the other half is green with the title "Date". The globe rotates for every thing that happens.
This theory introduced and seen in Bedtime Stories.