The guy, who had a huge French-style moustache and beard, was caught on CCTV and the police have released the image in an effort to find him.
Four friends enjoyed a fancy dress New Year”s Eve party at the Tudor Barn pub in Eltham, south East London and were just leaving at 2.50am when they were confronted by the mystery man.
He came up to one of the four, a 42-year-old man, and head butted him with no explanation or provocation.
His friend, a 28-year-old woman, tried to intervene but was thrown to the ground and held down by the suspect.
He was wearing a pink long-sleeved shirt and appeared to have been in fancy dress.
The motive for the attack has baffled the victims and the cops.
PC Martyn Peattie said: “These three victims all suffered at the hands of this man and have been left with injures that required urgent hospital treatment.
“This attack was completely unprovoked and I urge anyone who can identify the suspect to contact me. Any information will be treated in the strictest confidence.”
Anyone with information is asked to contact Plumstead CID on 07825 273811 or Crimestoppers on 0800 555 111.