Well, this didn't technically happen in one of the books, but in #21 Jake is yelling at David for morphing to lion in public, and Cassie reminds him of when he morphed to tiger and went jumping around on people's rooftops, and Jake's like "Oh, yeah." That sounds like a pretty dumb thing for Jake to have done.
Then, of course, there was the time in #14 (although, really, that entire book was pretty rife with examples) when they decided to demorph in the middle of area 51 and then just hang out for a bit because, hey, it wasn't like they were invading a top-secret government base or anything, right? Not to mention, that was the same book where Marco, Rachel, and Cassie used Fox Mulder, Dana Scully, and Cindy Crawford as aliases.