Phrase, circa 20th century.

Meaning: Rebuttal to a statement of romantic interest; a somewhat indirect way of stating that there will not be another date.

Other forms: "I like you, but I don't like you like you;" "I value our friendship too much;" "I had a great time, but I don't think it will work romantically between us;" et cetera.

Validity: Must be considered on a case-by-case basis.

Gender: Conventionally attributed to women, men have also been known to use this phrase.

Usage: This phrase is typically used immediately after a direct or indirect statement of romantic interest. This is the most correct usage. While this phrase has been used in situations wherein a significant amount of time (i.e. weeks, months, years) has passed since the first statement of romantic intent, this is not correct usage, especially if the user has engaged in activities that could be seen as signs of reciprocation of the professed feelings. (For more information on these kinds of activities, see Kissing, Holding Hands, Tender Gazes, and Sex/Sexual Intercourse.)

Correct:
"Would you like to go out to dinner sometime?"
"Oh, that's very sweet of you, but I just want to be friends."

"I had a great time tonight - can I see you again sometime?"
"I just want to be friends."

Incorrect:
"These past few months together have been so wonderful, and tonight - well, tonight you were just amazing... I love you."
"I just want to be friends."

"Do you take this (person) to be your lawfully wedded mate, til death do you part?"
"I ... uh ... I just want to be friends."