Probably the most well-known (and also the most painful) real implementation of a turing tar-pit is brainfuck. Some would claim INTERCAL is one too, but many would disagree since INTERCAL goes out of its way to make programming as hard as possible (roman numerals for I/O, that sort of thing).

Another fine example of a turing tar-pit, although in the domain of functional programming languages, is Unlambda.