But the 42-year-old resident passed away after being rushed to hospital with "massive internal bleeding".
Speaking after returning from his job as a teaching assistant at St Saviour's Primary School in Birmingham, Shabbir offered an apology to the deceased man's family.
The father, from Small Heath, Birmingham, said: "What I did was monstrous, but I am not a monster. There is no justification for what I did.
"I am deeply ashamed at my actions, even before I found out the poor man had died.
"Now I know that it makes it even worse, and my heart goes out to his family. I feel truly sorry and I completely regret what I did."
Hassan, who lives three doors down from Livingstone House where the ambulance had parked, claimed he waited patiently behind the ambulance for 20 minutes before losing it and writing the note.
He said he was coming home to switch cars and go to an appointment on Friday and that previous issues with parking on the street caused him snap.
He said: "I was coming home from work and had to go to an appointment on a different car.
"There was another guy waiting to come out of the drive but we were both blocked by the ambulance for 20 minutes.
"I just snapped and had a rush of blood to the head. I scribbled the note, rushed out and put it on the windscreen. There is no excuse for what I did. It was very bad.
"I knew it was wrong before a friend told me what had happened to the man in it. But parking here is very bad, and I've been blocked in before.
"I've been blocked by the police as well, not knowing where they are or what they are doing. There have been times I've been blocked from going to work. If I could take it back I would."
John Hagans, nurse consultant Livingstone House, a charity and rehabilitation centre for drug and alcohol addicts, told how the organisation was left "disgusted" by the note.
Hagans said: "We are completely disgusted by the note. Words fail me. This person deserves to be shamed.
"If the person who wrote it had had any idea of what was going on inside, they would not have dared.
"The resident collapsed in the home and was vomiting blood and our nurses and the ambulance crew battled extremely hard to save him."
Hagans said the patient had been at Livingstone for three months and was clean when he died.
He suffered an unrelated medical episode and passed away at Heartlands Hospital on Friday evening.
At the time, West Midlands Ambulance Service, as well as several paramedics, took to social media to express their dismay at the note.
The ambulance service tweeted: "Sometimes we just don't know what to say. This was the note left on an ambulance today.
"At the time, the crew were helping a man who was extremely unwell after vomiting blood.
"They took him on blue lights to hospital where he was in a critical condition. #patientscomefirst"
