I think there's a bit of a difference between being assertive and being pushy. At times you must be assertive to obtain the patient care you want - when you become a resident you may be suprised to find that "orders" you've written as sometimes just seen as "suggestions". Things don't automatically get done (or in a timely fashion) just because you've written something in the chart, signed and flagged it. Therefore, you DO need to be assertive (heck, this helps in all specialties) to make sure tests get done, interpreted, patients get their treatments etc. This not only helps patient care, but gets patients on the road to home quicker, which makes your life better.
You can be assertive - ie, calling the lab, asking rads when your study will be done/read, asking the nurses to do X,Y and Z without being pushy. Being pushy and rude is the LAST thing you want to be - you may also be suprised to find that things will get done SLOWER for those who are not well liked (especially if your position, such as resident, has NO bearing on someone else's evaluation/job position).
There are all types of surgeons out there and while we may have to be more assertive and appear to move faster and have less patience for wasted time, you don't have to be rude, arrogant and pushy.