When it comes to visiting someone casually, there are many different ways to describe the act. "Dropping in for" is just one option. Other phrases that are commonly used include "popping in," "stopping by," "visiting briefly," and "coming over." Each of these options adds a slightly different nuance to the act of visiting. For example, "popping in" implies a sudden and unexpected visit, while "visiting briefly" suggests that the time spent will be short. Ultimately, the choice of words will depend on the context and the relationship between the visitor and the person being visited.