Their problem. Not mine too.
However, I do speak Singlish too. Just for the convenience of communication. Imagine if you go to a hawker centre and speak proper English? You'd most likely have to repeat yourself a few times in order to get your message or order across. Language is a medium for communication. Black cat or white cat, if it can catch a rat it's a good cat. Singlish or English, if it can get the message across it's a useful language.
For example:
Customer A: Wei, char kuay teow mai hum one plate, want chilli.
Hawker Assistant: OK.
Customer B: Excuse me, I'd like to have a plate of pan fried noodles without cockles but with chili.
Hawker Assistant: Huh? What cocker? Talk what cock?