Poor "fatso" must have not been used to the idea of being a
"Manager" and probably had no experience in "face to face" dealings
with customers.
How on earth did he get this position ?
Could the "Fatso" be the "Head Chef" being rotated into the
Restaurant, to take over the "face-to-face" dealings for the day or
week. Pity him and the customers for that duration.
Was the "Fatso" a Singaporean ?
Perhaps your complaint would have been best addressed to the
Restaurant, then at least he is aware.
There is no harm in Visiting the restaurant again, if the food is
good and the price is acceptable. Ask the other Service Staff about
the "Fatso", who probably would also have given the other staff a
bad time too - unless, of course, it just happen to be the "Fatso"
off-color on the day of your visit.
If the "Fatso" still remain offensive, during your second visit,
you can always ask for the Head of the Restaurant - if it is not
the "Fatso" - or ask for the Owner's Address, for a formal
complaint to be made.