Spurious precision and unnecessary jargon: Saying in a talk that “this is a function of that” rather than just “this depends on that”. The latter: Fewer words; exactly the same meaning; “is” is only a weak verb-to-be while “depends”, despite its English meaning, denotes action and therefore carries the greater power.
That, and no one, least of all a real mathematician, is fooled that someone knows their stuff simply by their saying the words “mathematical function”. Or as a beloved TV character once said: “The impact has magnitude equal to one minus the exponential of negative i times 2 pi”.