唔好意思 is more like "excuse me" or a more polite form of "sorry" meaning use as making a mistake at a workplace for example: 唔好意思, 我而家去改 ( Excuse me (or Sorry), I'll go change it) or can be use literally ... "excuse me" asking people for example: 唔好意思, 廁所係邊到呀? (Excuse me, where is the toilet?) 對唔住: meaning use as "sorry" this is more like "sorry, I regret for what I did" ... is more like a formal way as way but really depends on how you say it or the situation for example: if you lost your friends favourite jacket 對唔住呀, 我整唔見左你的外套,我唔係有心嫁 (sorry, I lost your jacket, I didn't do that on purpose) using "對唔住" can also use as "sorry and ask for forgiveness) in Cantonese, "對唔住" is more serious than "唔好意思 " however, it really depends on how you say it or the situation but, it's ok for using as the same meaning... 唔好意思... sorry my explanation is kinda bad ... haha

Both ‘唔好意思’ (m4 hou2 yi3 si3) and ‘對唔住’ (deui3 m4 jyu6) can be used to show that you are apologetic about having caused someone problems or unhappiness. They both are commonly used. Which one we would use generally depends on how big or serious a problem we think we have caused to someone, or how unhappy we have made someone become. ‘唔好意思’ is usually said when we’ve made a small mistake while ‘對唔住’ is said to convey our apologies when what we have done is so wrong or badly, or has caused a lot of trouble to someone. The example situations in which I would say ‘唔好意思’ to you are as follows: (Note that ‘對唔住’ is also an alternative.) 1) I forgot to return the book to the library for you. 2) I carelessly spilled some water on your trousers. 3) l’ve lost the pen you lent me. (The pen is an ordinary one and isn’t a gift from anyone.) The example situations in which I think ‘對唔住’ would be more appropriately used are as follows: 1) I carelessly crashed my car into someone’s car and caused damage to it. 2) I’ve lost someone’s notebook which they need it when revising for the coming exam. 3) I talked back to my parents. We can put an adverb/adverbs of degree, such as ‘好’ (hou2) and ‘真係’ (jan1 hai6), which mean ‘very’ and ‘really’ respectively, before ‘唔好意思’ and ‘對唔住’ to express that we’re so sorry for what we’ve done. ~ 真係唔好意思 ~ 真係好對唔住 ~ 好對唔住 Please note as this reply is too long for italkie to send out for me, I put the remaining part of it in ‘Add a comment’ section.

如果你想表示你嘅歉意,可以話"對唔住",而"唔好意思"同"excuse me"差唔多意思