Net-speak abbreviation for need to pee. Be not fooled by its seeming rarity. Though you will not often need to pee during a conversation, when nature calls, you will be ready to make haste with this acronym. Much more descriptive than the generic BRB, this lets you know that your friend is important to you, and only the crushing pressures upon your bladder can tear you away. "Fear not my friend! I will return shortly." BRB simply does not hold that promise.
Contrast with the usual dishonesty of ROFL.