C180 pilot reported observing an NMAC between two other aircraft in the pattern resulting in one aircraft taking evasive action to avoid a collision.

Narrative

I was overhead ZZZ airport at 3500 feet for teardrop entry to runway XX. I observed this event and heard the radio calls. A Glasair was turning base to final and a Pipistrel was on final having flown a bigger pattern. Note: the traffic pattern was full of aircraft.The pilot in the Pipistrel made numerous radio calls that the Glasair was cutting him out of the pattern. He told the Glasair to 'go around' while holding his final approach heading and pressing closer and closer towards the Glasair. The aircraft appeared to be less than 300' apart when the Pipistrel finally executed a go around. The pilot of the Pipistrel then made several unprofessional radio calls calling the pilot of the Glasair 'an idiot; and I'll see on the ramp about this.'It appeared to me that the pilot of the Pipistrel could have safely executed a go around after making his first radio call about the traffic conflict with the Glasair and this whole incident would not have occurred. Instead he held his position on final; pressed on towards the Glasair while making numerous radio calls on an already busy Unicom frequency.After landing I approached the pilot of the Pipistrel and found him to be very angry about the incident. I allowed him to explain his side of the incident and told him I would get the pilot of the Glasair for a debriefing. The pilot of the Glasair and I introduced ourselves while the pilot of the Pipistrel said his name and that I am a CFI-I and you can find my last name on the report that I'll be filing'. The CFI-I was quite aggressive in his side of the event while the pilot of the Glasair accepted responsibility for not seeing the Pipistrel on final and not hearing the radio calls due to the aggressive and unprofessional attitude of the CFI-I we completed the debriefing and disengaged. This incident highlights the importance of CFI's setting a good example in the air and on the ground. The pilot of the Pipistrel could have gone around early; made professional radio calls and conducted a friendly debriefing on the ground."