Singaporians, without a doubt.

Jump lines.
Talk loudly in their sing song voices.
Pile their plates high with food at buffets, but never finishing.
Bargain for one tenth of the asking price.
Taking up 2 coach seats per person.
Mock local culture.
The worst are those singaporians that travel in large extended
families.....grandparents, spoilt brats, maids, and the boorish
peasant cousins........