Singapore has been seen as arrogant for a long time.
In 1973 (Google News Archive Search ) the Financial Times's Asia Correspondent noted that "it may also be dangerous for Singapore to become too arrogant" and noted that most foreigners found the State "insular and arrogant".
2 decades later Chinese business partners of Singaporean investors also found them arrogant (Google News Archive Search ).
Simply put, in many ways Singapore is a victim of its own success.
Having come, according to the official memoirs of its Founding Father Lee Kuan Yew (LKY), "from Third World to First", Singapore and Singaporeans believe that the Singaporean way of doing things is not just good but the best.
Undoubtedly Singapore does things well. It is clean, efficient and economically prosperous - notably compared to its neighbors.
And all this has been achieved relatively quickly; of the 31 years from 1960 to 1990, Singapore's GDP grew at 7% per annum or more in 23 of them (The Economic Growth of Singapore).
This has led to an attitude (or perceived attitude) to its neighbours that sometimes borders on contempt, summarised by a Malaysian politician as thinking "the city state [is] the best, the most beautiful and intelligent while others are dirty, backward, bad and faulty" (Google News Archive Search).
LKY famously said that without good government, Singaporean women would "become maids in other people’s countries, foreign workers" (5 Quotes From Singapore’s Lee Kuan Yew). Given that there are many maids and foreign workers in Singapore who come from Singapore's region, this was telling evidence of a certain disregard for those countries and their peoples.
It is fashionable to bash politicians for all of a country's shortcomings, but non-politicians also have similar sentiments (Google News Archive Search). They "tend to believe the Singapore way of doing things [is] the best" and can come across as contemptuous. They also pay less attention to "face" issues (Mind the Gaps) or simply, buttering up the other party.
Malaysia is probably the country with which Singapore has the closest (love-hate) relationship with. That two having been one country until 50 years ago only serves to complicate the matter: in many ways, Malaysia is seen as a cautionary tale of what Singapore could have been, and Malaysians are seen as "lazy, corrupt, insecure and backward" (of course, Singaporeans are seen as "greedy, arrogant, godless and boring", but that is a separate story). Singaporeans also engage in bad behavior when they go to Malaysia, like speeding and littering (https://digital.library.
Singapore's success is also in many ways due to its neighbours' failures. The aforementioned maids and foreign workers provide cheap labour that keeps the economy humming. The ASEAN scholarship that Singapore gives out to ASEAN nationals is seen as "'poaching' the creme de la creme of our youngsters" (The Great Malaysian Brain Drain) and accelerating brain drain in the region. This can seem like a slap in the face to other countries.
There is probably some jealousy mixed in here too. Singapore is small: a Chinese island in a sea of brown, and has less history and culture than its neighbours (Realism and Interdependence in Singapore's Foreign Policy). Despite that, it is so successful. There could also be post-colonial sentiment mixed in too, since the 1996 study (Google News Archive Search) found that Chinese people took Westerners' criticisms better than Singaporeans'.
Of course, it's not like other countries take all this lying down. Singapore has famously been described as "A little red dot in a sea of green" (highbeam.com A Little Red Dot in a Sea of Green; Foreign Policy and National Identity), an "irritating pimple" (Google News Archive Search) and snot (Snot flies in Taiwan-Singapore row).
