Normally, you would use "are" after two nouns. For example "exercising and eating well are healthy activities," or "working hard and saving money are important habits." So you are correct in your understanding of when to use "is" or "are." "Breaking and entering," though is a sort of exception, because "Breaking and entering" is considered a crime, singular. The more technically correct way of saying this would be, "The act of breaking and entering IS against the law." That's what we actually mean when we refer to "breaking and entering." I'm not a lawyer, but oddly, from what I understand of watching a lot of Law & Order, "breaking" a lock is potentially a crime (vandalism), and "entering" without permission would be another (trespassing), but "breaking and entering" is a specific crime in and of itself within the US criminal code. Because it is considered ONE crime, is is a singular act that *is* against the law. As you probably already know, the rule of is/are is different if the conjunction is "or." In that case, the verb "to be" must refer to the noun that's closer to it. So, "Either hot dogs OR pizza is being served" is the correct way to say it. And "Either pizza or hot dogs ARE being served" is equally correct. But if both are being served, then you say "Both hot dogs AND pizza ARE being served."