He He "Bullocks"

OK this is ambarassing. My continous habit of being curious to know new things or just say knowing exactly what something means got me into an ambarassing situation. I asked my co worker, a senior guy "what does BULLOCKS" mean. He laughed and said "how can tell this to you without making it less ambarassing"...said it means men's balls...gosh all these years i thought it means something like stupid or cow. See i am from India. My english is not bad or say not that great. So, yeah that was ambarassing, my face just turned red. Gosh...these slang words are used so commonly...How do you know without asking someone?