Umm...I haven't heard of either as slang, and I'm not sure where you heard this, but neither makes much sense. The only time I can think off where I would hear "Enjoy your clams" would be if I were about to eat clams (type of seafood). "Clams" was also a slang for money a long time ago (like around World War II), but it's very dated. "Enjoy your calms" is grammatically incorrect. One could say "Enjoy *the* calm" meaning a time that's tranquil (knowing that it will get hectic soon), but "Enjoy *your* calm" doesn't make a lot of sense.