A London startup, Rentify, were trying to replace every photo returned by the Tinder API over their network with their CEO's face when they discovered a secret value showing the success rate of a user's photo. Full marks for fun office hack originality. 0 marks for Tinder for not using https for their photos.

A friend of mine also discovered Tinder was returning dates of birth to calculate age client side, so was able to predict other user's star signs: https://medium.com/haralds-notebook/tinder-should-probably-f... It proved fairly effective at getting a reply, as you might imagine. Thankfully he had the decency to explain how he guessed.