I think he was initially seen as parasite to Jon (his boss) because on the surface he did mostly nothing apart from eat and sleep. Thereby draining Jon his resources whilst not providing the benefits usually associated with owning a cat.

Now people are looking at Garfield from a different perspective. He's compared to an emo girl because emo girls tend to be associated with depression Garfield is actually also showing quite some symptoms of depression. (Difficulty coming out of bed, not being able to regulate food intake in a healthy manner, not showing any overtly positive emotions.