Sad
Explanation
This comic delivers a visual pun built on the word "reflect."
In the first panel, one character asks another "What's wrong, man?" The second character, who appears to be a green-skinned creature (possibly an orc or ogre), responds that he keeps wasting his life and doesn't know how to change. The first character, a red-haired man, offers seemingly earnest advice: "That's because you don't know how to... reflect."
In the final panel, we see the green character is actually a vampire -- and the punchline becomes clear when we see him sitting in front of a dark computer monitor. He says "Not right now, Dave." The joke is that vampires, according to folklore, have no reflection -- they cannot see themselves in mirrors or reflective surfaces. So when his friend suggests he needs to "reflect," the vampire takes it literally: he can't reflect because he physically has no reflection. The dark monitor that should show his image shows nothing.
The humor works as a double meaning: "reflect" in the self-help sense means to introspect and examine your behavior, but for a vampire, the inability to reflect is a literal physical limitation. His existential crisis about wasting his life may in fact stem from this inability -- he literally cannot see himself, and therefore cannot self-examine.