"platonic" is a polite way to say you are only interested in friendship and not romance/flirting. as in:
about you: "I'm looking for platonic/friendly relationships, I am not here to date."
saying to someone: "My feelings toward you are strictly platonic."
or as apologizing: "I'm sorry if it seems like I'm flirting, it's not my intention at all!"
I hope that answers your question :)