He was given a chance to return to his house and family members had attempted in vain to bring him inside.
Judge John O'Connor said he would leave the accused without a conviction if he sat and alcohol awareness course.
O'Brien, with an address at St Patrick's Avenue, Dalkey, pleaded guilty to public intoxication at Railway Road, also in Dalkey on October 12 last.
Sgt Peadar McCann told the court gardai were called to St Patrick's Avenue where the accused was "in an extremely intoxicated state" while trying to walk his dog.
His sisters were there, attempting to get him to return home.
Gardai also told him to do so, but a short time later he was seen still out in the same state. His sisters were again trying to get him back into his house but "to no avail".
He was arrested for his own safety.
He had previous convictions for similar offences.
The court could see that "alcohol and Mr O'Brien are no strangers", his solicitor Ronnie Lynam said.
On the night of the incident, he had consumed "a couple of bottles of wine and also some vodka".
He lived around the corner from where he was arrested.
"He had been out walking the dog but he was in no fit state to be even out on his own, never mind walking the dog," Mr Lynam said.
The court heard the accused was living at home with his mother and three sisters.
He was on job seeker's allowance.
Judge O'Connor said he wanted O'Brien to take an alcohol awareness course.
If he did this, the judge said he would strike the charge out. If not, he would "deal with it in another way".
He adjourned the case for the accused to take the course.