After asking an expect, this question seem to be common knowledge for people in the comp. geometry field. The bound is quadratic at worst(for n and m edges of the 2 polygons we can have O(n*m) segments, and there is a construction that makes the bound tight) and the example follows: ![enter image description here](
It is 2 "hair combs" with n and m teeth , and the one is rotated by 90 degrees.