VivaSync

Tiffany Haddish recently said she was ready for the next chapter of her life post-DUI, and seemed to signal what that looks like this weekend at Seth MacFarlane's holiday shindig.

The actress/comedian was on hand for SMF's annual Christmas party Saturday night at the Pacific Design Center in West Hollywood, where the man of the hour shared the stage with TH at one point to let her do her thing ... namely, an original cabaret-style song.

Check it out ... in video, obtained by TMZ, you can see Tiff belting out an old school sultry ditty that she said would make Sexyy Red and Lil Kim blush -- AKA, this one's naughty.

The crowd sure seemed to love it ... and why wouldn't they? Fact is, Tiffany absolutely killed it. Now, naturally, Seth himself sang some songs as well, and yes -- he rocked the house with his old Sinatra-style crooning too ... just like he always does.

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