Someone told me that Saint Patrick never drove out snakes from Ireland, that there were no snakes there in the first place to be driven out.
Instead, he drove out metaphorical snakes meaning sinful things. Apparently a group of african twa pygmies travelled to Ireland, where when they couldn't be converted, Saint Patrick had them killed. Making him the saint who drove the snakes out of ireland.
Is this true? Seems like bullshit
It's bullshit. There was no direct contact between sub-Saharan Africa and Europe until the 15th century, except by way of Jerusalem during the Crusades.
Some scholars have tried to place Coptic Christian missionaries from Egypt in early medieval Ireland, but this theory is no longer taken seriously.
In these cases, furthermore, contact was positive. Spain attempted to forge marriage alliances (non succeeded); the Ethiopians sent monk-ambassadors to Rome and established a Church there; the Kingdom of Kongo adopted the insignia and titles of the Portuguese heirs to the Knights Templar.
There is a whole lot of yucky treatment of non-European/non-Christian/non-"orthodox" ('heresy' is a slippery thing)/non-male people in the Middle Ages, but this story is bullshit.
Let's underscore the assessment of /u/sunagainstgold - this is a lame if not contemptible fabrication (this story provides just a little bit of a racist edge to St. Patrick). But it is worth exploring this just a bit further.
On snakes: there were no indigenous snakes in Ireland before St. Patrick. The legend giving him the role of expelling the snakes was an after-the-fact explanation for this gap in the Irish ecosystem. Snakes were simply not able to get there because there wasn't a land bridge at the right time to allow snakes to achieve that sort of diffusion.
More importantly, the idea that there was an indigenous population of small people in Ireland is a common attempt to explain the persistent belief that the fairies - the Irish sidhe or "wee" folk. The belief that there must be some truth behind every legend is just that: it is a bit of modern folklore with nothing to substantiate it. Legends exist without necessarily having anything valid behind them, but the folk belief persists (and accounts for many of the questions in this subreddit!).
The idea that there must have been a smallish indigenous population living in Ireland before the arrival of the Irish has persisted as a way of explaining the widespread belief in diminutive fairies. But if that sort of explanation were needed for Ireland, then we would need it throughout Northern Europe because the idea of these supernatural beings, often living underground and often diminutive, is ubiquitous. There is simply no archaeological or other evidence to support the idea that these sorts of people lived there.
But for those who seek these sorts of explanations, the next task has always been to find the small people who might have been there at some early point in prehistory. It is easy to connect the dots - even though the dots cannot realistically be connected - so that a group like an African population must have in Ireland. But in fact there is no evidence of Africans or anyone else in Ireland or elsewhere who were small and then who were part of some persistent folk memory that turned them into fairies. Legends are not necessarily based on some phantom truth.