They are generally used in different situations Cut in: When a car gets ahead of another car and then pulls into the lane, forcing the second car to slow down. "The guy cut right in front of me on the highway." This also works with people in a line (queue) Also used when a couple is dancing and one man asks the first if he can dance with the woman - in the middle of the song. The man usually asks "May I cut it?" "Break in" Force ones way into a house or apartment to rob it. "Someone broke in last night and stole my sound system." Also means interrupt. "We were talking when Sam broke in with the news that he was getting married."

If there's a line a people waiting to be served, to cut in is used if you go ahead of someone that was there before you. The term, "Cutting in line" refers to this. It's never a good idea to cut in line and fights can start if someone does it. Cut in can also be used if there's a conversation and someone rudely starts talking over another person. They're cutting the other person off and have therefore "cut into" the conversation. To break in usually means personal property has been disturbed. A thief breaks into places to steal things. For example, "Someone broke into my car and stole my radio!" "My house had an attempted break in, but the alarm system went off and the burgular ran away."