One of the websites that I visit from time to time is Catherine’s excellent womenlearnthai.com (which she has very nicely said can be used by men too ;)). A while back there was a conversation which discussed the appropriate use of pronoun used to describe one’s self.
I play it safe and use ผม, and wouldn’t naturally be able or would want to use the cruder กู. I hear guys use กู much more frequently than is suggested by the language books. This is my take on it – it’s very similar to the usage of ‘saya’ and ‘aku’. The Thai กู (‘kuu’) and the Malay ‘Aku’ are not really rude, but they are certainly crude, informal and unrefined.
You wouldn’t teach a foreigner to refer themselves as ‘aku’, would you? Perhaps some would, I dunno, teenagers with their
penpals internet chat friends of the same age perhaps, but certainly, in a more civil and polite society, to have a foreigner use ‘aku’ word would be frowned upon, if not objectionable. I would argue that for a well-intentioned foreigner who would want to learn Malay in order to get access to certain functions of the state (for example routinely conversing with government staff at the various public departments for form-filling matters and such) it would be highly inappropriate and counterproductive to use ‘aku’.’ Saya’ would be perfect. It’s not overly polite nor does it come across as too stiff – it’s just right. There are now few people apart from those I have already known from school/university days that I would address myself as ‘aku’ naturally.
Going back to comparing Thai and Malay, it’s also easy to relate to how Thais use the word เรา (we/us) as we do this as well – ‘kita’. The last time I used it was when I was about 12 though. It’s somewhat too ‘cute’ to be used a personal pronoun after that.
Finally, dropping the pronouns entirely, too, isn’t all that uncommon. The context of the sentence would make it fairly obvious at most times to whom it refers to.