Falkirk man John Spears (60) attacked his victim in the Railway Tavern in Falkirk in March last year and left him scarred for life.
It was stated the victim had earlier been annoyed Spears was chatting to his mum in the pub.
Spears pled guilty to assaulting the man to his severe injury, permanent impairment and to the danger of his life.
He appeared for sentence at the High Court in Glasgow on Monday before judge Lady Stacey.
The court heard Spears’ victim, who also comes from Falkirk, had been out with his mother celebrating her birthday at the Grahams Road pub and became irate when he saw Spears talking to her.
Prosecutor David Taylor said: “This interaction appeared to upset the victim, who was heard shouting ‘He’s dead. I’m going to kill him’.”
At last orders, Spears walked over to the bar, smashed his tumbler on it and then thrust the broken glass into the man’s neck.
Mr Taylor added: “Mr Spears held the broken glass up at the man’s face and neck. He then drove it into him striking him on the right hand side of the neck as the man struggled to free himself.”
The incident was caught on CCTV.
Spears was put out the back door of the pub and was traced by police later that morning.
He immediately told police: “It was me. They called me a paedo.”
Defence QC Donald Findlay told the court Spears has an alcohol problem and has undertaken counselling.
Mr Findlay added: “His expressions of remorse and contrition are undeniably genuine. He does not understand how this came about. He went into a pub to buy cigarettes and a remark was made to him. He took offence and went beyond what was permissible.
“In his role as a shop steward he represents union members at tribunals. He did not intend any harm that night, but has issues with alcohol. He is a pleasant, courteous and respectful man.”
Addressing the painter and union official, who represents workers at industrial tribunals, she said: “What you did that night was very dangerous. I’ve read letters from your employer and the union of which you are an official.
“You should be setting a good example to others and not ending up in court. However, you have taken steps to address your abuse of alcohol. It is alcohol that has caused you to be violent on three occasions.
“The social worker who compiled a report on you says that your problem can be contained in the community.”
Lady Stacey ordered Spears to perform 300 hours unpaid work in the community, fined him £750 and ordered him to be monitored for two years.
She said: “I’m going to impose a fine as well just to bring it home to you your behaviour is totally unacceptable. This means you can carry on being the useful member of society you usually are.”