Commonly found variants; note these may range from acceptable alternatives to non-standard forms or incorrect spellings*.
* Singlish is a largely spoken creole, and as such descriptivism (recording forms that reflect actual pronunciation in spoken language, or as appearing in the linguistic corpus) is more pertinent than strict prescriptivism. Nevertheless, the use of more standard forms (or for words originating in languages with Latin script, such as Malay, accurate to the original spelling) is recommended and encouraged.

also can:

flustrate

flustrated

English:

flustered

+

frustrated

expand for details Detailed etymology

definitions

adjective

  1. flustered and frustrated; stressed; vexed; agitated; confused; in a state of panic

usage notes

The verb 'flustrate' is possible but relatively rare, though it has existed in English for a few hundred years (albeit mostly as an alternative form of fluster).