When does big, surpass too big, and enter grotesque?

So my trainer wants me to concentrate on my biceps. Despite the growth in chest, shoulders and traps my biceps have not made any real noticeable gains in size.

Now, avoiding the pitfalls of having to buy all new pants thanks to an increase in the girth of my quads is one thing. However, I have no qualms about seeing all my shirtsleeves rip at the seams should my arms balloon up, but again there is a fine line. While Mr. Coleman here may have some might big arms I find them rather too too much....