Nottingham Crown Court heard that Humphrey, 27, angrily asked Mr Rovet "If you're such a good friend why did you poke my missus?"
Sending someone a virtual 'poke' on Facebook is often seen as a way of flirting with them.
Prosecutor Gareth Gimson told the hearing the argument came to a head as the taxi stopped in Top Valley, Nottingham.
He said Humphrey struck 29-year-old Mr Rovetto, causing him to bleed from the nose - then delivered the fatal blow, knocking his friend to floor and causing him to bang his head on the pavement.
Father-of-one Mr Rovetto, of Arnold, Nottingham, suffered devastating head injuries and died in hospital hours later. Humphrey fled the scene but later handed himself in to police.
The court heard the friends had enjoyed a stag do in Mansfield before falling out. Mr Gimson said: "The taxi driver recalls Scott Humphrey was accusing Richard Rovetto of contacting his girlfriend in the past and doing so via Facebook.
"The expression used is a 'poke'. Scott Humphrey said to Richard Rovetto, 'If you're such a good friend then why did you poke my missus?'
"Richard Rovetto said he didn't know it was his girlfriend. The exchange became more heated." Humphrey, of Bestwood Park, Nottingham, admitted manslaughter and was jailed for four years and four months.
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