Is it correct to prohibit the phrase "BRB," used as an abbreviation for "be right back," due to its resemblance to the word for God (Rabb) in His saying, "Say, 'I seek refuge in the Lord of daybreak'"?

There is no apparent reason to prohibit that, and the aforementioned abbreviation has no relation to the names of Allah except in the resemblance of letters. Even if the meaning alludes to the name of Allah, there is nothing in that to indicate prohibition.