Callum Ward, 25, was seen “pressing” himself against the emergency vehicle before “simulating a sex act” on the hood.
Official police logs show an officer who saw him stated: “It looks as though he is attempting to make love to the front of the ambulance”.
Ward was drunk and had taken cannabis and amphetamine and was “in relatively high spirits” before the incident in November in Barnstaple, Devon.
He was first spotted setting fire to a packet of peanuts inside a phone box before mounting the ambulance, Barnstaple Magistrates Court was told.
He was found guilty of being drunk and disorderly and in possession of Class B drugs.
He was sentenced to a community order with a supervision requirement for six months and ordered to pay £60.
Ward, of Barnstaple, told the court: “I did start using drugs and drinking. I have seen the error of my ways with that.”
In 2007, Robert Stewart, of Ayr, Scotland, was placed on the sex offenders’ register after being caught trying to have sex with a bicycle.