Tara Reid was quick to accuse someone at a Chicago-area hotel bar of drugging her … and that guy tells TMZ the allegation is total BS.

Sean P, the YouTube influencer Tara referenced in her police report, tells TMZ … he met her at the hotel bar late last Saturday night … and they got to talking and traded contact info, before she invited him to go outside to smoke a cigarette.

He says Tara was initially standoffish, taking a dig at him for being a YouTuber … but when he shot back at her about the infamous TMZ video where she got denied entry at a Hollywood club back in 2006, her demeanor suddenly changed, and she got friendlier.

Sean P says Tara appeared “tipsy” — he says he was too — but they were both coherent enough to hold a conversation.

He says Tara asked him to go out for a smoke, and they did … and when they went back to the bar, he tried to close out his tab … when Tara handed him her purse and asked him to take out her room key. He says he looked inside the purse and saw pills. It was then Sean P says Tara screamed for security.

He says security arrived, asked if there was problem, and they both said “No.”

Tara was taken to a hospital, where we’re told the staff did a test for drugs. We do not know the results.

In her police report, Tara claims Sean P texted Tara videos of her the next day, which she believed was an extortion attempt … but Sean says he was only giving her a heads up his friend had video of her as she was rolled out of the hotel on a stretcher.

Sean P says after he sent the video, Tara accused him of slipping a roofie into her drink, which he denies.

A rep for Tara says … she never claimed Sean P was the one who allegedly roofied her, but she isn’t surprised by his “inaccurate” account.