Scientists
Scientists
[Cueball is staring at an empty box on the floor.] Cueball: In what scientists are calling "pretty gay", I can't find my shoes.

This comic plays on the type of statement that news reports often use: "in what [group of experts] are calling '[quote]'," to add more weight and credibility to their stories. In this case, Cueball is using the phrase to attempt to add gravitas to the (relatively mundane) fact that his shoes are missing and he thinks it's "pretty gay" by assigning this opinion to scientists (rather than it being, presumably, his friend's or his own opinion). The same joke is at play in the image text where a leading expert thinks the situation is "retarded."
There may be a second level to the joke: Randall was still working for NASA at the time the comic was posted, so his friends at that time would presumably include scientists and "leading experts." If his friends made fun of him for not being able to find his shoes, it would therefore be accurate to say that scientists had made those statements. However, since their being scientists is irrelevant to the legitimacy of their opinions about Randall's shoe problems, presenting their teasing as an expert opinion is humorously misleading; a similar joke is at play in 1206: Einstein .
The phrases "pretty gay" and "retarded" are infantile and offensive slang for "foolish" or "contemptible," and so they are the opposite type of speech expected of experts on news reports.  (These terms were not generally considered more than mildly offensive by most of the public at the time this comic was posted; the cultural mainstream is now typically much more critical of this type of language, and this comic would likely be heavily criticized if it were published today.)
[Cueball is staring at an empty box on the floor.] Cueball: In what scientists are calling "pretty gay", I can't find my shoes.
