The "ICUP" spelling joke is a playful and often childish way to trick someone into unwittingly saying or spelling out a word that sounds like a bathroom-related term. It is a simple and light-hearted prank typically used among friends or in informal settings.

Here's how the joke typically works:

1. Person A asks Person B, "Can you spell ICUP?"

2. Person B, not suspecting any mischief, spells out "I-C-U-P."

3. The response "I see you pee" is then humorously pointed out by Person A, revealing the prank and potentially causing laughter or amusement among those involved.

The humor in this joke lies in the fact that the spelling of "ICUP" sounds similar to the phrase "I see you pee," which is often seen as a mildly embarrassing or silly topic. It relies on the innocent person falling into the trap and unintentionally participating in the joke.

It's important to note that this joke is considered very basic and may be seen as juvenile or immature by some individuals. It's always essential to consider the context and the relationship with the people involved to ensure that everyone is comfortable and receptive to this kind of humor.