The 1985-86 Boston Celtics went 50-1 at home (40-1 in the regular season and 10-0 in the playoffs) on their way to an NBA title. It's the best home record in league history.
The 2015-16 San Antonio Spurs are currently 29-0 in their own building. They're 52-9 overall, an .852 winning percentage that puts them on pace to finish 70-12, which would be the second-best record of all time (behind the 1995-96 Chicago Bulls who played .878 ball and went 72-10).
Unfortunately for the Spurs, their near-record pace is 3.5 games behind the insanely good Steph Curry and the 55-5 (.917) Golden State Warriors. Like San Antonio, Golden State is also undefeated at home this year (26-0). Not only is there a chance the Spurs will post a better record than all but one team in NBA history and still enter the playoffs as major underdogs in their own conference, there's also a possibility San Antonio may win every home game it plays all season and fail to take home the title.
The Spurs could make it all the way to Game 7 of the Western Conference Finals vs. the Warriors (and lose) without dropping a single home contest. Depending on how many road wins they get in the early rounds, that scenario might leave them anywhere between 48-0 and 52-0 in San Antonio.
Golden State can also break Boston's 50-1 mark, and has the potential to end up from 49-0 to 57-0 at home. The Celtics' record is in jeopardy either way, but the prospect of the Spurs having a perfect home season and not winning a championship is somewhat mind-boggling.