'Macintosh Sucks' (sometimes shortened to 'Mac sucks') is a statement said by many smart people to reference the sucking of Macintosh computers, It is used to make fun of the sub-human race of Mac-Fags who thinks that Macintosh computers are actually good.
Mac-Fag: Hey, I just got a new computer.
Human: Oh really? What type.
Human: Macintosh sucks.