I was waiting to board a Southwest flight from Dallas to Midland a couple of years ago, and immediately after they started boarding they abruptly stopped the process. ABout 10 minutes later they announced that the delay was due to "passenger sickness," but that they were now ready to finish boarding.

While they had put garbage bags over the three seats on the left of the aisle about 6 rows back, the reek was was still very sharp and identifiable. I felt very sorry for those with high boarding numbers who ended up in the adjacent rows. The flight attendants were much more subdued on that segment, I remember.