When I write I'll try to be proper but if someone goes overboard the call will be "Man Overboard". I'm not sure anyone would react to "Crew Overboard". A vessel will always be a she and I always use the proper traditional gender on board but since I started looking at equipment a few years ago and it took me a while to figure out what COB was the first couple of times I read it I thought I'd get with the program.
A funny story about the first MOB instance I experienced. I was in the Navy on our first night out from Bremerton. We weren't even out to sea yet still in the Strait of San Juan del Fuca. About 0200 and I had the watch down in our shop. I was reading and the PA (1MC) clicked on, "Man Overboard, Man Overboard astern...." my first reaction was "he didn't say 'this is a drill", my second reaction was a bit stronger "Oh s@#t, he didn't say 'this is a drill". We shaved a minute and a half off our best time in getting the ship mustered. Turned out some joker threw a light stick overboard thinking it would be funny. Bad conduct discharge for him. Nice to know all that drilling works when it's the real thing even though it turned out to be not the real thing.