The topic of using "to talk/ to speak" in combination with "bad" has been discussed in detail on the
- to talk bad about somebody
North American informal for "to talk badly" about somebody
- to speak ill of somebody
rather British than American; not very common; formal or old-fashioned
- to speak bad of somebody
rather British than American; even less common; formal or old-fashioned
Phrasings that are rejected by native speakers as slang, bad style, or simply wrong:
- "to speak bad about somebody"
"'to speak bad about someone' may well be common in the USA, but it's appalling English." (a British LEO user)
- "there is nothing you can say bad about him"
(doesn't even work when replacing "bad" by "badly" or "bad things")
- "Now that she says bad about me, they will talk to her"
an example taken from a tweet - probably it was meant to be "bad things" and the "things" were sacrificed due to the limited number of characters
- "a few of the things that the president has said negative about people"
politely dubbed "wacky grammar" on the LEO forum