What does i can see what you had for breakfast mean?

The phrase "I can see what you had for breakfast" is a playful and metaphorical way of saying:

* You're acting a certain way that betrays what you ate. This is usually used humorously to imply that someone is behaving in a way that suggests they had something particularly stimulating, sugary, or unusual for breakfast.

For example, you might say it to a friend who is acting particularly energetic and talkative.

* You're being obvious about something. It can also be used to suggest that someone is trying to hide something, but their actions give it away.

For example, you might say it to someone who is trying to hide a messy breakfast, but crumbs are falling from their clothes.

In both cases, the phrase is not meant to be taken literally. It's a playful way of pointing out someone's behavior and the potential cause.