Some go off and choose other advisors, because they feel they want or need have more one-on-one attention and face time. I wish them well, generally. One hopes they find what they are looking for and in any case are not embittered. I believe the Wiccan expression is "merry meet, merry part, and merry meet again".
Some hover in my doorway, hesitant to come in, and ask "are you busy?". (The answer is that I am always busy, but I would not take someone on as an advisee if I wasn't prepared to spend time with him or her.)
Some barge right in, even when other students are sitting in my office, or jiggle the handle even when the door is closed and locked and they have already knocked. (This last one is a pet peeve of mine, especially because it's disturbingly loud from inside the office.)