It's from the 2004 Harley and Ivy mini by Dini and Timm (also whence this post's icon). Issue 2. Harley and Ivy have gone to the rain forest to pick up a rare plant called the Zombie Root. Ivy, obviously, loves it there. Harls...not so much. It's raining, and there are huge bugs - and she's just squashed one on her cheek, getting great amounts of bug goo on her, which made her lose her lunch.
After fetching the Zombie Root and...eh...communing with nature...Ivy goes back to join Harley, and notices that she's absolutely miserable. Cue a kiss on the cheek (despite the puke and bug guts), 'cheer up baby', and a promise to be back in Gotham soon, so Harley can stop being wet and miserable.
The series is REALLY worth reading, BTW. (Checking Amazon, it's collected into a volume which also includes Judd Winick and Joe Chiodo's Love on the Lam, which is also a fun read.)