The process of learning Arabic is quite unlike the process of learning many other languages due to the fact that one must distinguish between Modern Standard Arabic (MSA) and colloquial Arabic. The former is utilized in news broadcasts, newspaper articles, etc. while the latter is the essentially the language spoken at home.
I highly recommend that those seeking to study Arabic tackle Modern Standard Arabic prior to any sort of colloquial Arabic for the simple reason that MSA can assist with building a solid foundation through which one can expand his or her knowledge. Just think of MSA as being the trunk of a tree while Egyptian Arabic, Maghrebi Arabic, Levantine Arabic, Gulf Arabic, etc. as being the ancillary branches. With that said, I am most familiar with Levantine Arabic and thus I do want to provide some words and phrases from the dialect that some might find useful. As an aside, many of these words are also found in MSA as well (although the colloquial words might be pronounced differently depending on the region). So without further ado:
The word “نحس” refers to bad luck, misfortune, or a jinx. Since you tend to find a lot of idioms in colloquial Arabic, if you were to associate someone with bad luck, you might want to say:
“إيده نحس” (eedo naHs), which literally translates to “his hand is bad luck”, but essentially means that the person is unlucky. In addition, one might say:
“وجهه نحس” (wujho naHs), which literally translates to “his face is bad luck”, but basically means that the person is a jinx.
“شك” means doubt or suspicion and it often may be used in the phrase:
“ما فيه شك” (ma fi shakk) or “بدون شك” (bidoon shakk), meaning “no doubt”. Alternatively you could say something like “لا شك أنك رح تيجي” (la shakk anek raH teejee), which translates to “there’s no doubt that you’ll come”.
So those are just a couple words (and the phrases that might accompany them) for those who are interested in Levantine Arabic.