The 25-year-old hurled a glass into the crowd after an audience member appeared to criticise his behaviour towards host Katherine Ryan, to whom he had earlier directed several lewd comments.
The spectator called him “misogynistic” during his acceptance speech as he accepted the award for "hero of the year" at the O2 Brixton Academy event.
The furious rapper responded by telling his critic: "Thank you for ruining my speech," before tossing his microphone at him.
After the man threw the mic straight back, slowthai lobbed his champagne flute and launched himself off stage. He was held back by security following a brief tussle.
The music fan’s comment was an apparent reference to his exchange with Canadian comedian Ryan, who he called "baby girl" while making a number of suggestive remarks.
— Vinesh (@V1nesh)February 12, 2020
After later being confronted by a member of the audience, the rapper shouted: "Misogynistic? I stand for equality... if you can't take a joke, sit down."
Earlier in the evening while on stage with Ryan, Slowthai urged the host to “smell my cologne” and said “smells good don't it.” Footage from the event showed him put his arms around her and say: "She wants me to tend to her flowers."
Hours before the awards ceremony and ensuing altercations, the 25-year-old ominously tweeted the word "SEX" followed by a flower emoji.
Ryan, who has been praised for how she handled the situation, joked as the rapper left the stage: "You are like the hottest guy I've seen," adding: "You are younger than my babysitter."
Taking to Twitter following the exchange, Ryan wrote: “He didn’t make me uncomfortable. This is why we need women in positions of power."
She continued: "I knew he had lost from the moment he opened his mouth like any heckler coming up against a COMIC - not a woman - a COMIC.
"I was operating 2/10. What a sweet boy. I defused it.”
He didn’t make me uncomfortable.
This is why we need women in positions of power. I knew he had lost from the moment he opened his mouth like any heckler coming up against a COMIC - not a woman - a COMIC. I was operating 2/10. What a sweet boy. I defused it.
Tonight was fun! ❤️ https://t.co/BBMPZpIvhy— Katherine Ryan (@Kathbum)February 13, 2020
Fellow social media users shared their outrage at the incident, with one tweeting: "Slowthai just ended himself in ten seconds flat."
Another added: "Slowthai really released a clever, sincere, politically inspired banger of a debut album then shat all over it by creeping on a presenter."
And another wrote: "If anyone says ‘He’s had a drink’, you need to check yourself & your mentality. As always (Ryan) handled the situation, but imagine if it was someone not as quick or confident? Absolutely disgusting."
The Standard has approached slowthai’s representatives for comment.
The Northampton rapper, real name Tyron Kaymone, won best collaboration for his work with Mura Masa as well as his hero of the year award, which is voted for by the public.
Known for his controversial statements, he made headlines in September for holding up an effigy of Boris Johnson's severed head at the Mercury Prize ceremony.
During the eyebrow-raising performance of his hit 'Doorman', he stripped down to the waist and held the fake head aloft, shouting: "F*** Boris Johnson. F*** everything."
Mr Johnson laughed it off at the time, saying the rapper had actually said "back Boris" but was let down by the acoustics.
While somewhat overshadowed by slowthai's explosive display, this year's NME awards were otherwise a happy affair for a number of artists.
Taylor Swift was honoured at the ceremony, picking up the best solo act in the world award. She told the audience that thanks to a previous NME award she won she is now able to display two of the middle finger-shaped trophies side by side in her home.
The US pop star added: "This is like the craziest awards show I have ever been to, thank you."
In the other categories Little Simz picked up the award for best British album for GREY Area, while AJ Tracey won best British song with Ladbroke Grove.
The best album in the world award went to Lana Del Rey's Norman F***ing Rockwell, while best song in the world went to Billie Eilish for Bad Guy.
Best British solo artist went to FKA twigs and best British band was chosen as The 1975.
US heavy metal band Slipknot won the best band in the world gong.
Also honoured at the ceremony was Glastonbury organiser Emily Eavis.
After being presented with the award, she said: "I watched my dad pick this up when I was 16-years-old and I was like, I will never do this festival and I'm in so deep, there's no getting out of it."
She dedicated her award to "all the female artists".
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