The Las Vegas-born 41-year-old, who is hoping to become a permanent resident, first came here in 1997. He returned in 2007 and has stayed ever since.
He told The New Paper: "My American humour and sarcasm didn't translate all the time, and I was talking too loudly. I had to speak in a less direct way and also listen more."
Tonelli and local actress-host Rosalyn Lee are the hosts of new Channel 5 reality TV show Steady Lah!, which tests foreigners on their knowledge and adaptability to the Singaporean lifestyle.
The show will premiere on March 28 at 8pm.
Tonelli was pleasantly surprised by the variety of food here and is now hooked on laksa, popiah and kaya buns.
But he misses the portion sizes back home.
He said: "You could spend $10 in America and be really full. But when you buy Western food here, the portion size can be quite small, so you can be hungry afterwards."
He admitted his tastes have changed, to the point where he finds American desserts "jelak" (Malay for cloyingly rich).
There was the local dating scene to navigate too.
Tonelli, who previously dated local actress Joanne Peh, said one of the challenging aspects of an inter-racial relationship is adapting to your partner's culture.
He added: "You are constantly learning about each other, good and bad. So I've learnt things about myself that I need to change, for example in communication, so it works better in a relationship."
He has been with his girlfriend, Indonesian Tata Cahyani, 41, a single mother of two who works in the jewellery industry, for about three years.
He now speaks a bit of Singlish and his favourite phrases are "wah lau" and "can lah".
When asked how Singaporean he has become, he said: "I just won't queue, that's the one Singaporean thing I cannot do.
"And I don't 'chope' seats with tissue paper. But I am 'kaypoh', because I like to find out what people are up to."
The story first appeared on The New Paper on March 18, 2017.