refers to a situation in which an undesirable candy bar in a vending machine is blocking access to the desirable candy bar behind it.
Dammit! I was jonesing for some peanut M&M's but I got choc-blocked by that Almond Joy bar that's been sitting in front of them for the past three weeks!
Preventing your friend from eating too much chocolate, which leads to break-outs, fat butts, and cottage cheese thighs.
Not to choc-block you, but do you really need that truffle?