In the Maltese Language, Haqq Alla
is the most common swear word, and is also quite offensive to the Catholic religion, as it is translated to "fuck god".
When saying to someone "Qisek Haqq Alla", that can be translated literally to "You are like a 'fuck god'". In other words, you're comparing the person to a swear word, and thus you're describing him as being offensive, disrespectful or totally not in place just a swear word such as Haqq Alla
This phrase is quite offensive both to the person you're telling it and also to anyone who is hearing it.