After some heavy tinkering, I must have screwed up my R installation and some package permissions. Rather than try to fix it, I just want to wipe and reinstall everything. So I did:
sudo apt-get remove r-base-core
sudo apt-get remove r-base
sudo apt-get autoremove
Which did uninstall R, except when I reinstalled R, my old packages were still available (and some of them were causing troubles).
How can I do a complete reinstall, including removing all packages, except for the included base library?