How can I stop Skype launching when I start my computer and telling all the in-laws to bombard me

[MrsFogi]

It is driving me insane and there doesn't seem to be anything in the preferences to change the original settings that I set up when I installed Skype (ie launch when I log in and tell me contacts when I am online). I can't cope anymore - everytime I work at home my mother-in-law and DH's uncle bombard me with calls and I simply don't want my ILs to know when I'm at my desk and when I'm not.
Btw I'm on a Mac in case that makes a difference.

I presume that Skype is in your Dock? If it's not start it so that it is.

Right click on it's icon (CTRL & Click if on a one button mouse) and see if "Open at Login" is checked, if it is uncheck it.

You can also change your preferences so that you are not shown as being available. So, your Skype is on and if you want to use it, you can. No one can "see" you so they won't bother you.