I tend to look first at the face; if he's cute, then I proceed to a quick body glance. A crotch assessment is only viable when the guy is wearing gym shorts/sweatpants/etc.; they may have a jeans ***** or something but those can be quite deceiving, take it from me
I'm not really into ass too much, but I'll sneak a peak if that's all I can get. Otherwise, face is the biggest factor for me. After that, they have to be at least semi in shape (not necessarily muscular, just not really overweight). I love smiles and eyes (shape is important; for color, brown and green are my favorites). I'll be honest though, when a hot sweaty stud is freeballin and I can make out a nice fat piece of meat....
