Defendant Warren Culshaw was out celebrating his 50th birthday but turned on his victim outside the Cedar Tavern in Cedar Square, Blackpool on December 14.
Preston Crown Court heard drunken Culshaw had been asked to leave the venue but came back in shouting.
He then launched what Judge Christopher Cornwall described as a “terrible attack”, raining at least six blows on his victim.
Culshaw, who admitted wounding, had claimed the victim had made a remark about his partner - but the victim insisted it was not the case.
The court heard Culshaw’s victim suffered such a severe fracture to his cheekbone and eye socket that medics are unsure whether it is safe to operate.
Judge Cornwall, jailing Culshaw for two years, said: “As you stand before this court in your suit you do not appear to be a violent man.
“But when you are drunk you are a very dangerous man.
“You have no control whatsoever over yourself or your actions and you think nothing when drunk of using considerable unlawful force against others who you claim have offended you.”
He added: “This had been a perfectly amicable social gathering.
“You became drunk, you had to be asked to leave the pub.
“You seem to have done devastating injuries to his left eye.
“Almost every aspect of his life has been changed for the worse.”