One thing I really don't like is people tampering with creeds. Creeds are meant to be statements of what the Church as a whole believes. So the church as a whole agreed the Nicene Creed at Nicea (well, actually at Constantinople, but it was based on one they'd agreed at Nicea), then the Pope decided to add the word "filioque" (meaning "and the Son") after "who proceeds from the Father". It caused a big split in the church.
Oh and here's the original form of what is now known as the "Apostles' Creed". This version seems to go back to the 2nd century AD, which is pretty early.
I believe in God the Father almighty;
and in Christ Jesus His only Son, our Lord,
Who was born from the Holy Spirit and the Virgin Mary,
Who under Pontius Pilate was crucified and buried,
on the third day rose again from the dead,
ascended to heaven,
sits at the right hand of the Father,
whence He will come to judge the living and the dead;
and in the Holy Spirit,
the holy Church,
the remission of sins,
the resurrection of the flesh
(the life everlasting).
There's two sources for that, which are word-for-word the same except that they're in different languages. That last line is in one of the sources and not the other one, but otherwise they're identical.
Since then, however, some people have seen fit to add other bits onto it. Some of them (like calling God the Father "creator of heaven and earth") are fine - that line is just taken from the Nicene Creed. Some of them, like "he descended into hell" are debateable, haven't been held by all the church everywhere always and just cause arguments.
What really annoys me about this though is that the Reformation was meant to be largely about rejecting all the bits the Roman Catholics had added to the faith of the apostles, but they kept the creeds as the Romans had them in the 1500s, with all the extra bits added. Grrrr...