How to correct egg nog that is too sweet?
1) Too sweet, you could dilute it with some rum or other alcohol. That might mask the sweet aftertaste with an alcoholic aftertaste....

2) Grate some nutmeg on top: fresh nutmeg has such a bite, your tastebuds will forget about the sweetness.

3) While you're at it you could further dilute it with a little half and half, or just plain milk.