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3.
1. awesome; incredible; great; fantastic
-can also be used as-
2. horrible; useless; bad quality
3. Interjection
That was a smacking performance!

What smacking sound quality...

Smack that!
by The Indian Nerd:Akshaya (jk!) March 25, 2010
 
1.
When someone has taken ecstacy and after the energetic facet of the drug has worn down, the user feels like they want to sleep. They could even sleep on the ground in the middle of the city. Usually comes as an after-effect of a really energetic night then a few hours later you feel really tired. Probably because the energy is coming from no-where and your adrenal glands are putting out energy they don't have.
'What's wrong man?'
'Awww fuck I'm smacking hard.'
by Erin Hellyeah May 28, 2008
 
2.
slang term for making out.
I was standing beside this really hot guy watching paint dry and we totally started smacking on one another.
by Kiryk July 03, 2012
 
4.
The noise you make when you are kissing.
Have you kissed Mandie? She is such a smacker when she kisses. It's so hot I love it, I wish all girls made the smacking noise. I like smacking my lips.
by mandie sinnott October 21, 2007