Unfortunately, some of the Google Suggest suggestions are offensive and Google had to filter the searches related to pornography, violence, and hate speech. Google's over-protective algorithms now filter all the suggestions that include "is evil", "I hate", "[ethnic group] are" (for e.g., "chinese are"). Suggest also filters "Smells Like Teen Spirit", name of a popular Nirvana song.
"Queries in autocomplete are algorithmically determined based on a number of objective factors (including search term popularity) without manual intervention," explains Google. Suggest's filtering flaws are more obvious, now that Google Instant previews the results without having to press Enter. If you type [google is e], Google no longer previews the results and suggests to "press Enter to search".
Google Blacklist (not safe work and potentially offensive) lists some of the rules used by Google to censor the list of suggestions.
[Thanks, Alex, Waxy.org]