Rob Kardashian -- NOT A DADDY!

Rob Kardashian is NOT a daddy ... he's intentionally punked the media by tweeting out some not-so-cryptic hints he's a father and then watching the lies spiral out of control online.

Sources VERY close to Rob tell TMZ ... Rob was testing the media Thursday night by tweeting, "Was with my baby mama tonight." In July, he tweeted, "Happy I got my Son with me for the 4th tomorrow."

Various outlets immediately took the bait, but here's the thing ... there is no baby mama and no baby.