The American Council on Exercise has categorized ranges of body fat percentages as follows:
Description Women Men
Essential fat 10–12% 2–4%
Athletes 14–20% 6–13%
Fitness 21–24% 14–17%
Acceptable 25–31% 18–25%
Overweight 32-41% 26-37%
Obese 42%+ 38%+
In the OFFSEASON bodybuilders may bulk up to 20% - especially endomorphs.
155lb @ 5'10" even at 4% BF (which is almost impossible to reach without drugs and a very restrictive lifestyle) is not bodybuilding.
If a 5'10" guy competed in the under 160lb class he would be half a foot taller than everyone else.
155 @ 5"10" is too skinny at any % BF - look at Brad Pitt in fight club 5'11" @ 165 - he looks great, but at no point is he like a bodybuilder, his thighs are about as big as my arms!
Pitt
If you want to look like that then all cool - that's achievable!
ACE has poor standars then. Different gov sites have Obese for men at 25% so I was off a bit.