Is it safe to discharge my body's static electricity onto my MacBook Pro? Often in the winter (low humidity), getting up from and sitting down onto the seat at my desk, or taking off a jacket, and such will build up a static electric charge on my body.  Sometimes I don't remember to touch a metal object before touching my MacBook Pro, causing me to zap my laptop.  Is this likely to cause damage?  Should I be very careful to discharge before touching my laptop?
That shouldn't be a problem at all if your MacBook is connected to the power source since it's grounded and by the way I wouldn't consider harmful to touch the MacBook body after being electrically charged even if the MacBook isn't connected to the power source. You have to pay attention only if you're touching directly motherboard components.

EDIT

My answer is not completely correct.
Check the comments