A fine result of Jon and Liz's recent dating developments is it allows jokes on the topic of Old Friend Hates Buddy's Changes in Behavior Over Significant Other. This plays beautifully in Garfield because the characters and relationships are already set up for it. Jon's desperate and eager attempts to please a woman at all cost to personal dignity and comfort flow naturally into a man totally pussy whipped, even by a woman making few if any demands. Today all Liz has to do is call him, and Jon bends over backwards to be attentive, even as he brazenly violates his friend's comfort zone and lies to Liz. It's also a sweet observation about how exciting new relationships are, but in Garfield it's always tinged with the ominous undertone: Jon overcompensates because he's love-starved.
Garfield is just as naked as Jon, of course, but chalk it up to joke logic. Besides, it's funny that Garfield would complain about having to look at Jon's scrawny, soapy body, finding it more disgusting than his own robust physique, that he holds Jon to certain human standards of decency while he allows himself to pick an choose. Even better it tells us something about mutual understandings in Jon and Garfield's domestic situation. Maybe not much, but at least that Garfield has divested himself of at least one more normal cat behavior, that mysterious love of staring solemnly at their naked owners.
Also Garfield's phrasing "could you do nothing with a towel on?" holds the awareness that it may be a given that Garfield is a chronicle of inactivity, but at least it's not usually waving its crotch in your face.