Male BFF's are usually the biggest culprits for pussy locking their female friends, because they secretly fancy them, and don't want them fucking anyone else but them. Ex boyfriends can also create a pretty unbreakable pussy lock if you happen to be partying in the same venue.
"No, it wasn't. You kept pussy locking me! I never cock block you! Why do you keep doing this to me?"
"Because I love you......."
(shocked look of absolute disgust)
"........as a friend."