Taking vacations days in the middle of a semester
In the departments I have worked in, it would probably be considered unprofessional to leave on a pleasure-cruise in the middle of the semester. I suspect that that is universal. 

In other words, this is not the image you want to project as someone who will still have to go through the tenure process. On the other hand, it's a fairly small thing -- people are gone all the time, although almost always for professional reasons: at conferences, workshops, for collaborations. So the mechanics of being gone are all appreciated in any department, such as moving classes around, giving out reading assignments instead of in-person classes, or putting a midterm exam on such a date and having someone else proctor the exam. Students also understand these things. In the end, it will be a judgment call: It comes over as "frivolous" to leave for a vacation and cancel classes over it, but it's also not a huge deal and I'd be surprised if anyone would think that you'll lose tenure over it. It's just a bad mark in your peers' perception of your professionalism.