many interpretations can be derived from the saying top shelf
1. something is pretty shit hot.
2. to describe material of a sexually explicit nature that is stored in the highest point of a shop.
and my old favourite;
3. to describe a female as being rather atractive in a sexully stimulating way
1. that shot you took was top shelf old boy
2. that dirty old cunt reads from the top shelf
3. A:"fuck me she is top shelf! marks out of ten i'd give her one."
B:"not half! woof!"