Mint, I am always amazed how much joie de vivre you have, puts me to shame. I try hard not to swear, as I know I don't really know when and how - though I do know ras de bol, j'en ai marre, etc, learnt in one of my French lessons before I arrived here, but never used!
You are quite right, register is important, I have a book, Using French: a guide to contemporary usage (Cambridge U Pres about 2000 ... which is all about about register ... and which words to use. I decided at that point not to worry about what level I spoke, but to go for the middle of the road stuff, which has served me well enough. It all depends on age, sex, geographical origian, and indeed your "class" to abbreviate ... fascinating, but I'll stick with what I can cope with.
But bravo to you for trying all this.
I have to agree, ce m'est egal is most useful in all sorts of occasions!
ex W1, via 47 and 11 and now [just] in 34, equidistant from Carcassonne, Narbonne and Béziers, where I hope we'll finally stay!!