Bong Water in the Sink

Similar to Beer under the bridge:

When one or more stoned individuals either physically or verbally spars, and the next day they agree to forget about it since they were so high.

Nikki: "I bet Joe was mad about me yelling and hanging up on him last night when I was baked out of my mind."

Kristin: "He was toasted too. He said forget about it - it's bong water in the sink."