The term 'bog standard' means average or ordinary, or something slightly worse than that. The term was first noticed by the authorities in the 1980s, and has since experienced a rocket-launch to fame. Nowadays it can be found on hundreds of witty webpages dedicated to toilets of some sort.
Bog, you see, is British slang for toilet, although the original and still current meaning of the word is swamp. Neither did much to help the negative connotations swarming to the words, like mosquitos to a quagmire. However, the origin of the word may be somewhere else entirely.
According to people who speculate about these things, the term most probably comes from box standard, a description of something that has been manufactured a hundred times, that fits the box exactly and couldn't be less interesting.
Sir Clive Sinclair is recorded using it in a way that supports this view: "Luckily, we cannot foresee the day when a computer becomes just a standard box. There will be box-standard machines along the road, but we do not simply have to make those." Computerworld interview, February 1983.
The term had long been in informal use when it received its ladder to fame from the British Government in 2001. The Prime Minister's spokesman, Alastair Campbell, made a comment about "bog-standard comprehensives", and received much attention for it, as well as criticism from people in favour of the comprehensive school system.