I haven't gotten this since I entered Prestige, but when I was in my 40s my first run through I was spraying the big loading dock area on Vacant (M60, double-tap, deep impact) and somehow hit some C4 as an enemy ran out one of the doors killing him and one other. Shocked the crap out of me. I can only imagine how the other guys felt.
I don't think Bomb Squad shows explosives until you get relatively close. With the red lines showing on the Claymores I find it to usually be a wasted perk. If I hear a "click" from a Claymore I just sprint anyways. I only used it when I started over and didn't have Bandolier.