And the good-natured Poolburn farmer agreed with them all during his marathon run along the 152km length of the Otago Central Rail Trail in less than 24 hours, finishing on Saturday morning.
"The word had spread about what I was doing, and so many people all the way along told me what an idiot I was," Mr Sinnamon said.
"There were no arguments from me."
The 45-year-old athlete came up with the venture as a fundraiser for Sport Central.
He had never run so far or for so long.
Although the journey took its toll on his quadriceps and knees and he was hurting as he completed the run, there was still a smile on Mr Sinnamon's face as he reached Clyde.
He was greeted by about 60 well-wishers and another 20 accompanied him on the final leg of his trip, most joining in at Alexandra.
Mr Sinnamon is the Poolburn School board chairman and when he told school principal Simon Waymouth about his plans for the run, Mr Waymouth decided to see if other Otago schools would also support Mr Sinnamon's fundraising efforts.
Fourteen schools became involved and are staging their own fundraising activities for Sport Central.
Some of the schools are based along the rail trail; others are from as far afield as Millers Flat and Glenorchy.
Mr Sinnamon said he was humbled by the support leading up to and during the event.
His support crew included his wife Dianne, Mr Waymouth and Mr Sinnamon's brother-in-law, Martin Powley, of Clinton, who cycled along the rail trail as Mr Sinnamon ran.
Multisport athlete Tim Pearson and harrier and cyclist Janice Weatherall, both of Alexandra, also kept him company from Oturehua to Clyde.
Other cyclists and runners, including school children, also accompanied him for part of the trip.
"The other thing that kept me going, apart from those people, were all the people who came out to meet us along the way, and every stop in between," Mr Sinnamon said.
"That gave you a shot in the arm."
"I told everyone that I'd lost my bike and that was why I was running."
"Everywhere we stopped, people gave us money for the cause - it was overwhelming and a wonderful reflection of our community."
The total amount raised will not be known until later this week when the money from the schools has been added in.
He travelled at a average speed of about 8kmh and stopped for three meal breaks during the run.
He expected to finish in 24 hours and completed the trail one minute and 20 seconds ahead of time.
Mr Sinnamon has had three busy weekends in a row, beginning with the Goldrush multisport event, and then the Ghost to Ghost triathlon last weekend.
He is not ruling out a repeat performance of the rail-trail run - "I'd never say never."
To celebrate the feat, he planned to have a spa and then catch up on some sleep.
Otago Central Rail Trail Trust chairwoman Daphne Hull, of Alexandra, believed Mr Sinnamon was the first person to run the length of the trail, from Middlemarch to Clyde, in one go.
"I think it's very courageous to go out and attempt to do 152km nonstop - that's a huge challenge which requires determination, stamina and commitment.
"He's a great role model."
Sport Central co-ordinator Bill Godsall said it was a huge effort.
"It's great that the schools have got in behind it and that the money is being raised for a local sports trust," Mr Godsall said.
"What's even more important than the money is that it shows children what can be done if you put your mind to it."
