I have a gaming group in which this term "丑八怪"is being used a lot along with the 眼皮底下, anyway all the letters look similar.
According to this article:
In short, there were eight weird painters in Yangzhou, they were nicknamed 「揚州八怪」, The mainstream artists did not like them and some called them 「醜八怪」
醜 referred to their 'ugly style' -- some mainstream artists thought so
怪 referred to 怪人 (eccentric person)
In modern times, the term 醜八怪 is used as a derogatory term for "ugly person" or "ugly creature"
As for 眼皮底下 (literally means under the eyelids) has the same meaning as "under the nose" in English
"丑八怪" means An/the ugly person(s) acting in a strange/eccentric way/manner.
The direct translation of "眼皮底下" is "below eyelid", however, it really refers to "see" (看), as below eyelid is the eyeball that performs the function - see.
Let's try to put these two phrases together to make better sense:
"眼皮底下淨是丑八怪" = "放眼望(看)去淨是丑八怪" - "All I can see are ugly weirdos", or "Look around, all are ugly weirdos".