Meths is methylated spirit, or in layman's terms spoiled ethanol mixed with methanol. For an apt illustation of how low you'd have to stoop to be a meths drinker, watch 'Withnail and I'. There is a drinking game people have invented to accompany the film (you'd be mad to try it) which involves attempting to match Withnail drink for drink. I believe a shot of meths is the replacement for the moment Withnail drinks lighter fluid, the latter being too dangerous:
Marwood: Not even the wankers on the site would drink that. That's worse than meths.
Withnail: Nonsense. This is a far superior drink to meths. The wankers don't drink it because they can't afford it.
Withnail: [having just drunk a bottle of lighter fluid] Got any more?
Marwood: No. I have nothing.
Withnail: Liar. What's in your toolbox.
Marwood: Nothing.
Withnail: Liar. You've got antifreeze.
Marwood: You bloody fool. You should never mix your drinks.
I realise it's over-quoted by the student population, but it remains an awesome film, and judging by the title of a certain Morrissey album, one he likes too.