Why did my Chinese teacher describe Donald Trump as 口吐莲花?
「莲花出淤泥而不染」，象征纯洁 (lotus flower came from mud but not stained by it. Symbolizing purity.)

Your teacher described him as 口吐莲花 in an ironic way,  mocking his foul mouth

Idiom 舌灿莲花: 譬喻说话的文采和美妙 (&quot;the tongue sparks lotus flower&quot; refers to having the literary talent to speak beautifully.)

Again, ironically, your teacher was mocking his lack of literary talent and his incoherent speeches