It's mean to disrespect your friends dead parent.
Rick and Terry grew up together but haven't seen one another for years, until one day Rick stops by Terry's house.
Rick wants to reminisce with his friend about childhood memories.
Rick reminds Terry of a time when the two boys got into trouble together and Terry's father had to come get them out of it.
While they are talking, Rick tells Terry that he remembers Terry's father as being the most unlikable person he ever met.
Terry remembers the time fondly and the two men enjoy reminiscing together for the entire afternoon.
Terry is visibly hurt by the comment and Rick feels terrible as soon as he realizes how inappropriate it was to say that since Terry's dad is now dead.