In Quebec, the worst curses are offenses against the Catholic Church, which is (well, it was until the 60s, some decline since then) a huge influence upon the culture.
In fact, curses or swears in Quebec are called sacres, an ironic twist on the real meanings for sacred.
A couple that I know...
1. calice
2. calisse!!
3. chalice (the sacred cup of Mass)
1. Christ
2. crisse!!
3. Christ
1. tabernacle
2. tabernac!!
3. tabernacle (where the body & blood of Christ are kept, near the altar)
1. ciboire
2. ciboare!!
3. the ciborium, small dish on altar that contains the large "host" (body of Christ) eaten by priest during Mass
These might sound mild, but they have special meanings in the culture, I guess. Direct offense against the Church. If you are a kid and get heard blurting out one of these words, you'll be hauled around by your ear.
If they are chained together quickly, to make a nonesense phrase, then it is considered milder and mostly used for effect. ie "saint-cibouree de tabernac!"
you asked...