The Brief: "I'm baby" is a ubiquitous catch-all phrase that can refer to any connotation of the term "baby."

DEEP DIVE
The simple phrase “I’m baby” has become a viral meme, but what on earth does it mean?
By saying “I’m baby,” someone may be referring to how they are small, someone’s significant other, cute, or in other ways like an infant. It is semi-synonymous to smol.
The meme has caught on and is particularly popular on Twitter. Its popularity may be due to how it amusingly sounds like how an actual baby would identify themself, or because people are longing to return to the comfort of infancy. It is often used as a caption for cute selfies or thirst traps.
Origins
The meme originated from a news story about a teenage girl hiding from a home invader with her four-year-old niece. A picture associated with the story shows a text exchange between the 14-year-old girl and her mother. Part of it reads “I’m baby/call 911.” Those texts appear have been sent by the girl’s mother and “I’m baby” appears to be a typo. This screenshot was taken out of context distributed along with jokes and memes about a baby sending cryptic text messages.
It started from this girl who was like home alone and had an intruder in her home so she started texting her mom hfnfhdhez pic.twitter.com/vJIyCZPoeb
— mich (@bIueberrys) March 4, 2019
Then, this image was included in a nonsensical internet ad campaign, giving the meme an additional layer of random humor.
Memes
The phrase has since spread to many contexts and is often used as a sort of inside-joke for those who are amused by it or who recognize the meme.
Me explaining to my boyfriend why he can’t scold me: pic.twitter.com/hYR0ucimnv
— 𝓶𝓸𝓮𝓼𝓱𝓪 🐻✨🍒 (@Moeshayan) February 22, 2019
i’m baby, i’m baby, i am baby say it to me
— jaboukie (@jaboukie) March 18, 2019
yes im baby yes im gonna keep reminding u every five seconds
— sar (@heavenbrat) March 18, 2019
hey guys, i needed to get some stuff off of my chest so i wrote this little song. hope it speaks to you like it spoke to me. pic.twitter.com/u4qxyiLRva
— jack is in dallas (until august) (@JackWilliamRtF) March 1, 2019
fergie didnt raise us all for yall to be saying “im baby” like dumb weaklings.. say it with me: im big girl
— ★ 🆂🆃🅴🆅🅴🅽 ★ (@ishtiben) March 18, 2019
*cocks gun* how many times do i gotta tell u….. that I’M BABY.
— 𝖻𝗅𝖺𝗂𝗇𝖾🐰 (@boysblush) March 15, 2019
i’m? baby
you’re? baby
we’re all? baby
hotel? trivago— angel! (@softbxbie) March 16, 2019
I’m baby (no object permanence, incapable of sustaining belief that I’m loved unless someone is physically in front of me reminding me at regular intervals)
— rose 🦇 (@roselyddon) March 18, 2019
This is what I mean when I say “I’m baby” pic.twitter.com/VhQWwBQBvH
— madi g™ (@lizardluvr69) March 12, 2019