huh?

there are some phrases used in everyday life that i just do not understand.  they sort of send shivers down my spine.  maybe you can help me understand why people feel the need to use these phrases...

• could care less

example:  "i could care less what you make for dinner tonight, i am starving!"
my confusion:  i think this phrase represents that the speaker doesn't care about something but if you could care less about something doesn't that mean you still have a little bit of care left to give?  meaning you care about it a little?  meaning you don't not care?  shouldn't the phrase be "i could not care less" about something?

• i had to laugh at that

example:  "i just had to laugh at that because it was so something she'd say!"
my confusion:  is laughing that big of a chore?  "i had to" makes me think that the speaker didn't want to laugh, but they had to.

• that being said

example:  "he is really super nice and attractive and is going to be a doctor someday.  that being said i think you should stay far away from him because he is bad news."
my confusion:  saying "that being said" just gives the speaker permission to go back on everything they just said.  a huge contradiction.  why even say the nice things before?

am i just crazy or are these phrases odd to you as well?  really.  help me out.