The File Picker meme is an internet meme known to originate around /g/ or other communities where Windows users are at odds with Linux users. It pokes fun at the fact that the GtkFileChooser does not support a thumbnail view. This is usually accompanied by "it is <current year> and the GNOME developers still haven't added one" demonstrating that Linux is shit because of this.
In late April, 2004, a bug was submitted to GNOME's bugzilla, suggesting a feature to add to the GtkFileChooser, the main tool for picking files (to upload, open, etc.) within a GNOME desktop, a thumbnail view similar to that found on Windows. This bug has seemingly been completely ignored by GNOME staff.
A typical implementation of the file picker meme can go two ways. One way is to take the head-on approach, often greentexting a few lines, the first of which normally mentioning the year, the next pointing out that the file picker bug has not yet been fixed, then the next few lines implying that the lack of this feature means that Linux is inferior to Windows. Another approach is to pretend to be oblivious to the meme, and act as if the thumbnail view of the file picker is a feature that exists but he cannot find. With either method, one is guaranteed to attract attention from autistic Linux users who will stop at nothing to defend their operating system.
Though it is true that a GNOME-based desktop environment most likely uses the GtkFileChooser and as such will not have a thumbnail view, it is beneficial to point out that Linux is a kernel, and no matter what stance one takes on the GNU/Linux debate, Linux by itself will not have a graphical environment, let alone a file picker, and that the KDE Plasma Desktop Environment does in fact have a thumbnail view in its file picker, and that it is glorious. Using KDialog instead of the GTK file picker avoids this problem entirely. OpenSUSE and some other distributions use KDialog by default.