Projecting
Projecting
[Ponytail, Cueball, Megan, and White Hat are standing. Cueball is talking, with arms outstretched, palms up, while the other three are looking at him.] Cueball: Like a lot of you, I have a real problem with projection.

In this comic, Cueball expresses his difficulty with psychological projection . Projection is taking qualities of the self and attributing these qualities to others.
Cueball actually admits he has a real problem with projecting, but while doing so, he is seemingly oblivious to the fact, that he is stating this in a way that projects his self-identified difficulty upon his friends: Ponytail , Megan and White Hat . Of course, this could also just be a joke made by Cueball, as it is the joke in the comic. On the other hand, Cueball and Randall have serious issues with social interactions , and this could just be another example of such a problem.
In the title text, Cueball continues his projections, stating that this is something we all need to work on . So he continues to believe that all the others have the same problem, not just a lot of them as in his original statement, which left the possibility that not all of them had this issue. In the end, he also tops it by saying but especially you all indicating that he imagines his own case is a less serious issue of projection than that he actually projects the others as having.
Alternately, the phrase having a real problem with projection usually means the person speaks quietly, their voice doesn't carry very far, particularly in acting and public speaking environments. Someone with difficulty projecting wouldn't be heard by people in the back row, or perhaps even halfway into the audience (depending how much difficulty they have). This comic is notably smaller than the average xkcd comic, making it the visual / comic equivalent to not projecting. Just as a non-projecting voice cannot be heard very far away, this comic cannot be seen very far away (in either case, not as far as usual). Under this interpretation, the title text is referencing that his audience is also not projecting, they're just as small as he is.
Alternatively, Cueball expresses his difficulty with complex numbers .  There exists a common projection between the complex and reals, but it may not be clear to him about which method to use or how to do it.  If he is projecting onto the real part of the complex line, then his issue is a many-to-one problem, which explains why it is everyone else's problem as well.
An alternative perspective might be that the characters, as stick figures, are represented as two dimensional projections of three dimensional objects, and this projection has an issue that depth information is not preserved, so for example, it isn't clear whether cueball is facing towards us or away from us. As his arms are not foreshortened by the projection, this indicates that he is standing in an unnatural pose, so the fact that he says that especially the other characters have a problem with projection would be a good example of psychological projection.
A further alternative read could be that Cueball is acting as the Randall surrogate, noting that the other characters are projections of Randall's conscious and subconscious self.  The title text could then be read as either directed to those aspects as expressed as characters within the comic, or directed to the reader, who also has things to work on.
A different meaning of the term "Projecting" is seen in the fields of public speaking and drama, being the way that a person clearly uses their voice to address an audience.  If Cueball is not projecting well, then the characters listening to him may ignore him.
Projection is an ongoing issue.  People from disparate communities can experience this all the time, where one person assumes out of habit that the other person has the traits of their community.  On the end of the spectrum, projection can be completely delusional, as the comic hints at.  It would make sense for that be more common for people who attend less to where others are at, such as introverted or powerful people, two groups that experienced engineers can land in.
It is also possible that Cueball is addressing the portion of readers who feel the need to project onto Randall their own desire (and meticulousness in analytical searching) for layers upon layers of hidden meaning in xkcd comics. The assumption that he has stuffed several different obscure punchlines into the one sentence of a single-panel comic is, despite the layered punchlines in some other comics, quite a stretch. Randall may be suggesting that such projections from readers onto him are problematic because they cause comic explanation pages to be filled with rambling speculation that can make the explanation of the actual joke harder to understand.
[Ponytail, Cueball, Megan, and White Hat are standing. Cueball is talking, with arms outstretched, palms up, while the other three are looking at him.] Cueball: Like a lot of you, I have a real problem with projection.
