Bug-eyed monster

A bug-eyed monster was a generic term for an alien creature.

John called a Klepton a bug-eyed monster. (COMIC: The Klepton Parasites)

Sarah Jane Smith, during an argument with the Fourth Doctor, said that she was sick of, among other things, being savaged by bug-eyed monsters. (TV: The Hand of Fear)

Captain Cook acquired a set of two-headed coins from a bug-eyed monster on Leophantos. (TV: The Greatest Show in the Galaxy)

Ace once asked the Seventh Doctor why bug-eyed monsters always chose to invade Earth. (PROSE: The Left-Handed Hummingbird)

Sam Jones called a Janusian a bug-eyed-monster upon seeing it on the TARDIS scanner. (PROSE: The Janus Conjunction)

The Eighth Doctor, upon first seeing the Face-Eater, noted that UNIT would have called it a bug-eyed monster. (PROSE: The Face-Eater)

Clyde Langer, while distracting Lieutenant Koenig and his Nazis, claimed that he'd fought hideous bug-eyed monsters and defeated them all with his mobile phone. (TV: Lost in Time)

Behind the scenes
In Sydney Newman's concept for Doctor Who, bug-eyed monsters were to be avoided. Because of this he initially opposed the inclusion of the Daleks; however, they ended up ensuring that the series would be successful.