Dr. McCoy often calls Mr. Spock "pointy eared", and it isn't a term of admiration. Have any non-human characters made disparaging remarks about the physical appearance of humans or their behavior? For example, have Klingons called humans slippery-browed runts, or Trills called humans blank-faced half-persons or Vulcans called humans midget-eared hysterics? Even if such racial slurs are not used at the Starfleet level, is there any evidence that they occur among the general populace?
B'Etor (in TNG: Generations) expresses disgust at seeing Beverly Crusher's face up close.
B'ETOR: Human females are so repulsive.
Seska (in VOY: Basics) felt that our foreheads were decidedly inadequate, at least by Cardassian standards.
SESKA: Hello, everyone. What do you think of your son, Chakotay? He has your eyes, don't you think? Thank goodness he doesn't look too human. You all have such weak foreheads.
Armus (TNG: Skin of Evil) is quite unenamoured with our general physique.
ARMUS: You overrate your gift. You humans are puny, weak.
Worf (in DS9: Let He Who Is Without Sin) is very aware of our physical limitations
WORF: Which only makes it worse. Compared to Klingons, humans are fragile creatures.
A (holographic) Klingon expresses his true feelings about humans in Voy: Real Life.
LARG: I told you. Humans are weak, cowardly.
The Velaran "microbrains" from TNG: Home Soil clearly find us repugnant.
VOICE: Ugly, ugly giants bags of mostly water
Commander Shran (ENT) and other Andorians frequently call humans 'pinkskin' throughout the series. Only once does Shran stop himself and say 'human' instead.
Captain Solok, a Vulcan, also made it a personal mission to embarrass and humiliate Captain Sisko throughout his career, taunting him by calling him over-emotional and out of control. This during DS9 episode "Take me out to the Holosuite" (S7E04). Most Vulcans make it a point to call humans over-emotional (Tuvok to everyone, Spock to Kirk and McCoy, Ambassador Soval to every human he meets).
From ST:TOS "Let That Be Your Last Battlefield" - Commissioner Beal, speaking to Loki (Lokai?), refers to the crew in passing as 'monochromatic trash'.
From ST:TOS "Devil in the Dark" - The head of the mining team says that the Horta aren't so bad-looking once you get to know them; Spock then says that the mother Horta said virtually the same thing to him during the mind-meld - that 'she found humans unattractive, but though she could get used to them'.
From ST:TNG S1:17 "Home Soil" - The silicon natives describe humans as 'ugly bags of mostly water':