Mr. Johnston, son of Rose and Victor Johnston from Enniskillen, was killed at a house in Killesher in the early hours of Friday morning.
His 33-year-old brother Raymond has been charged with his murder.
Speaking at Mr. Johnston's funeral service at St. Macartin's Church yesterday (Wednesday) Rev. Kenneth Hall told mourners to think of his devastated family.
"David was a son, brother, grandson that was loved by his family and that is evident by the tears that have been shed in the last few days. I really don't think young people who are of a carefree mind realise how much pain and agony they put their loved ones through when things go horribly wrong.
"When school days passed he faced the real world making choices in life and not all the choices were his family's preferred routes to take. A wilder side of life may be okay to a certain extent, but when mixed with excess alcohol, can be a dangerous combination and this often leads to the downfall of many people," he said.
During his address, Rev. Hall appealed to young people: "It is not the chances we take it is the choices we make that determine our destiny."
Following the funeral service, Mr. Johnston was buried at Cross Cemetery.