A thug from Erskine scarred his friend for life moments after he dropped his phone.
Robert Dunn turned on David Beaton in Glasgow city centre's Trongate on August 23 this year.
The 23-year-old pounced while enroute to get Dunn's screen repaired after Beaton broke it.
The bleeding victim later required ten stiches to repair the facial wound.
Dunn pled guilty today at Glasgow Sheriff Court to assaulting Mr Beaton to his severe injury and permanent disfigurement.
The court heard Dunn tried to board a bus in the city centre around 4.20pm.
Mr Beaton - whose face was bleeding - alerted the driver not to let him on as Dunn had "slashed him."
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A 999 call was made and police traced the pair together.
Mr Beaton told officers he had been assaulted by Dunn who was then arrested.
The victim was taken to Glasgow Royal Infirmary for treatment.
Prosecutor Sarah Latta said: "He had a three-inch wound to the right side of his face which required 10 stiches which will leave a permanent scar.
"He told officers that he and Dunn were friends who fell out due to an incident here he dropped his phone.
"Mr Beaton said he would repair the smashed scree and the went to a shop nearby where they had an argument and Dunn slashed his face."
Officers later found traces of blood and the neck of a bottle where the assault took place.
Sentence was deferred until next month pending background reports by Sheriff Matthew Jackson QC.
Dunn remains remanded in custody.
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