I'm afraid the changeable nature of Arabic letters lead the other answer to look for a translation, where this is actually a transliteration, i.e. the Arabic spelling that would be pronounced (roughly) the same.
The text on the shirt is a transliteration of "Jinx". The characters here are:
ج ن ك س
which, from right to left, are J N K S. If you're curious, the J and the K change shape significantly when joined up here, and the N gets reduced significantly, to just a short upstroke and a dot.
If you want to play around with this, set Google translate to Arabic->English, and choose the 'marhaban' entry method, where English letters are mapped to Arabic. That's how I got the above characters, entering "j n k s", spaces included. If you leave out the spaces you get
which is what is written on the t-shirt.
As vowels in Arabic are frequently not written, but rely on the reader's familiarity with the language to tell them which vowels to use, it's possible an Arabic reader would read this as "janks", or "junks", or maybe accurately as "jinks" - I'm still at the point where I wouldn't be able tell.
And while it is possible to add "harakat", which look like smaller decorations around the main word, to make the vowel explicit, it's not usually done (e.g. in newspapers), and would make it look less cool, which is the whole point of wearing a t-shirt with your name in Arabic on it in the first place.