Arman Tsarukyan is taking his fight against Dan Hooker head-on -- literally -- 'cause he butted his opponent right in the noggin during a tense weigh-in altercation.

There's some serious beef between these two guys leading up to UFC Fight Night in Qatar -- Tsarukyan wasted no time going after Hooker after joining the promotion ... and it only intensified in the days leading up to the bout. Getty

The two came face-to-face on Friday ... and as they approached each other on the stage, Tsarukyan (22-3) jolted forward and made contact with Hooker's face.

The fighters were then separated ... but that didn't stop them from jawing at each other as they were held back. Getty

In case you don't know the lore with these dudes, Hooker (24-12) went OFF on Tsarukyan in an interview with MM

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