The term "pharisaical" is offensive to many Jews (me included) because it denigrates some of our most respected rabbis.
When Jews think of Pharisees, they think of the sect at the end of the Second Temple period (circa 0 CE) that became the basis for rabbinic Judaism. This group could be contrasted with other parties of the day such as Zealots (who wanted a war with Rome), Sadducees (the wealthier "Establishment" who accommodated Roman and Greek practices and denied certain religious tenets), and the Essenes (separatist/puritan types who withdrew from society). The Pharisees walked a middle course that did not like Rome, but did not want to start a war or withdraw from the world. They primarily wanted to learn, teach, and increase the piety of the Jewish population. Notable Pharisees from this time period would be Hillel, Shammai, and Yohanan ben Zakkai.
In contrast, when Christians think of Pharisees, they think of examples like Gospel of Mark, where Jesus argues with the Pharisees regarding him forgiving sin (which according to the Pharisees and thus Rabbinic Judaism to this day, only G-d can do). The Gospels of Matthew and Luke go further, listing various hypocrisies and portraying them as letter-of-the-law literalists without compassion. This distorted picture is very offensive to Jews who consider it early Christian anti-Semitic propaganda.
By analogy, imagine if someone you admired (I don't know who you like, say George Washington or Gandhi) had their name or title made a synonym for immoral or unethical behavior. Wouldn't you be offended too?
Copied from "English Language and Usage" Stack Exchange:
pharisee (lowercase) a sanctimonious, self-righteous, or hypocritical person.
pharisaic Hypocritically self-righteous and condemnatory.