Do not insult the weak?

I would say "weak at" eg I am very weak at mathematics,

Generally yes, though there are a few exceptions. Some acidic salts are weakly acidic but still strong electrolytes. An example would be ammonium nitrate

weak is not strong

meek, geek

Human saliva has a normal pH of 6.5 to 7.5, so it is essentially neutral but can vary from very slightly acidic to very slightly alkaline.