Sorry man, nothing against you and I'm not trying to put you down in any way, but it actually comes from the song "Almost Cut My Hair" by CSNY in 1970 (written by David Crosby). He sang "feel like letting my freak flag fly". The album was Deja vu. I don't know, but it's possible he got the line from somewhere else before he wrote the song. Of course, he's always been so stoned I doubt that he can remember lyrics from other peoples songs.
If I knew as much about other things as I do about music, I'd be a millionare.
All this shit is just stuck in my brain!