Being asked why you talk to yourself is a small humiliation, and lilacprincessx starts the poem right there. The speaker's answer is simple: "I have imaginary friends." The reaction is not curiosity. People "look at me weird and walk away." What the poem really wants to say comes in the next line, which is the heaviest in the text: they "never ask me the reason why." The rest is that unasked question being answered. Real people can be cruel, so the speaker has made companions who aren't. The central idea is that what looks odd from outside, a person muttering to nobody, may be a sensible response to being hurt.
The poem is free verse with no rhyme and no regular meter. It reads like speech, a person explaining herself in plain words. Almost every line ends in a comma, and the poem never stops for a full stop, not even at the end. I'd read that as the rhythm of someone who has to get the whole explanation out before the listener leaves. The final word, "mean," is left hanging with nothing after it.
The most noticeable device is repetition. "Imaginary friends" appears five times in fourteen lines, each time doing slightly different work. First it is a defence ("I tell them that I have imaginary friends"). Then it is the thing nobody questions. Then it is something that needs a reason, and finally it is a conclusion: "That is why I have imaginary friends." The phrase works like a refrain, as if the speaker is repeating it to make it harder to wave away. The vocabulary is just as plain. "Weird," "mean" and "nice" are schoolyard words, the blunt terms children use to sort people. The poem doesn't dress up its feelings, and that is where its force comes from.
There is a quiet irony in the way strangers behave. The speaker complains that real people don't understand her, and the first scene proves it. Those who ask the question walk away before the answer, so they enact the unkindness the poem describes.
The middle of the poem tightens into a short list: "They don't judge me, / They don't make fun of me, / They're nice to me." Two of the three lines say what the friends *don't* do. Their kindness is defined mainly by the absence of cruelty, and the one positive quality is the modest word "nice." The speaker isn't asking for much, just not to be laughed at. Since the poem begins with her "talk[ing] to myself," these friends may well be her own voice in other forms. That is my reading from the opening, not something the poem states. If it is right, she supplies the acceptance she can't find elsewhere. It makes the poem both sadder and more resourceful.
The ending changes the claim. Earlier the speaker says "sometimes real people are mean." By the last lines "sometimes" has gone, and "people" has become "friends": "Because real friends, / Are mean." The line break puts a pause before the verdict, so "Are mean" lands flatly. "Real friends" is normally a compliment, as in "my real friends stood by me." Here the phrase is turned inside out. "Real" no longer means loyal, and "imaginary" has come to mean safe. The title's two words have swapped their usual values.
The poem's significance lies in its candor, not in polish. It doesn't ask for pity or dress its hurt in elaborate imagery. It states a cause and an effect and leaves the reader to feel the weight. Many readers will recognise being judged on what looks strange while nobody asks what lies behind it. All we know of the writer is the name attached to the poem, and the poem doesn't need more. It makes one point clearly: the person who seems to be talking to no one may be the one who has gone looking for kindness and had to build it herself.