It really helps to have a plan when you're making a comic. In fact, if you don't have a mock-up, it's downright painful and you can flush a lot of valuable time right down the toilet.
I spent most of yesterday working on this strip, making up the dialogue as I went. Turns out there's a lot of timing involved in writing for comics, and while I think of myself as somewhat funny, I can't just pull snappy one-liners out of my ass (and who would want them then, anyway?).
The bottom (hehe, bottom) line here is that next time, I'm going to 1) prepare my scene and dialogue in advance and 2) do a rough sketchy bit to put everything in its place before I start.
PS. After all that, Libby ruins everything by ending her sentence with a preposition. Screw you, grammar!