Police detained Rob Smith, 54, on suspicion of criminal damage after he was spotted painting the box in Lymington High Street, near the gold medallist's home, in the early hours of Saturday morning.
The Post Office have been giving mailboxes a golden makeover in the home town of successful Olympic champions across the country, and have already resprayed one in the sailor's honour in Cornwall, where Ainslie grew up.
But Mr Smith, a father-of-three, was aggrieved that Lymington had not been similarly honoured.
Mr Smith, who runs a bar and restaurant in the town, was arrested by police as he completed the do it yourself paint job with two cans of car spray paint.
He arrested at the scene on suspicion of criminal damage and held in a police cell in Lyndhurst overnight. He was later released on bail.
A spokesman for the Royal Mail said: "We are extremely disappointed that someone has chosen to vandalise this particular post box.
"It is illegal to tamper with any of our post boxes and we are liaising with our engineers to ensure that it is repainted red as soon as possible."
On Saturday Mr Smith was unrepentant. He said: "When they said they weren't going to paint anything in Lymington, I just thought this is madness."
He said Lyndhurst should have been chosen as it is where Ainslie lives now.
Mr Smith, the owner of Haven Cafe, Bar and Bistro, said: "I did it because I'm a passionate sportsman, I think the Olympics have been brilliant, Ben's achievements have been outstanding.
"Everything about Ben is Lymington, he lives here, most of his sailing friends are based down here and for all of us that know him down here, we just wanted to say thank you for being the best sailor in Olympic history.
"We've got to recognise these people and say thank you."
He added: "All of Lymington believes that the Post Office made the wrong choice in painting one down in Cornwall, give him two."
It comes amid reports of a spate of cases where post boxes have been redecorated by residents in the home towns of medal winning athletes.
In Doddington, Lincolnshire, the post box has been painted bronze in honour of hockey player Georgia Twigg, who won a bronze medal with the Team GB women's hockey team.
Residents in Emsworth also decorated a post box with silver foil in honour of sailor Ian Percy.
The Royal Mail has now urged excited fans to leave the painting of postboxes to their staff.
A Royal Mail spokeswoman said: "We understand the sentiment, and congratulate the women's hockey team on their achievement.
"However we'd rather people left the painting of postboxes to us.
"We are liaising with our engineers to ensure that it is repainted red as soon as possible."
