Finishing 3rd would definitely be disappointing. I'm not so concerned about being a 'laughing stock' or what others might say, but unless United do amazingly, it suggests we have a pretty poor second half of the season. That would force some re-evaluation about how close we are to being the best.
I still think this discussion is premature though and have been amazed by how quickly some white flags have been raised when we are still level on points with a game in hand. If you offered an Arsenal fan this position when the news of Jesus' injury came out you'd have bitten their hands off.
Liverpool had 2 wins from 6 at one point last season, they also went 3 games without a win later on and still took the title race to the wire. The time may come for this discussion sooner than we'd all like, but let's not pre-empt it.