Old joke, which I read long before I knew what PADI and CMAS are, and thanks to the web and Altavista, I managed to find again:
This dive boat is going out to a dive site with a group of PADI and CMAS divers on board.
The boat starts to sink. The CMAS instructor looks at this and says "OK everybody, get your kit ready, might as well do a deep dive." And off they go.
The PADI instructor thinks for a moment and says "OK, everybody, we have a change of plan, please pay me $50 - we are now doing a wreck dive."

From this page I got this:
P.A.D.I Pay Another Dive Instructor
S.S.I Still Seeking Instruction
B.S.A.C. Bugger Surface Air Consumption
C.M.A.S. Can't Master Aquatic Skills
S.C.U.B.A. Some Come Up Barley Alive
N.A.U.I. Not Another Undrwater Idiot
I.A.N.T.D. Invest Another Thousand Dollars
O.W.S.I. Over Weight Scuba Instructor
P.A.D.I Pay And Die Immediately
P.A.D.I. Put Another Dollar In