Question: Why do some restaurants have table service but require you to pay a cashier instead of paying your server? There’s often a line at the register, and if you’re a single mom with small kids — like I am — it’s annoying to wait around. Then if you pay in cash, you have to go back to the table to tip.

Answer: I imagine they think it’s faster than requiring the waitstaff to take your check and bring you change in addition to taking orders and delivering food. This may very well be true for the waitstaff, but, as you point out, it often can be inconvenient for the customer. If paying by credit card is allowed, I find that’s easier — you can just write the tip on the receipt rather than returning to the table.

Q: On a recent flight I was seated behind two women who obviously didn’t know each other. At one point one of the women asked the other, "So, when is your baby due?"

Now, the other woman was not obviously pregnant. She just was wearing a loose, empire-waist top. Fortunately, though, she said she was about five months along, and they had a long conversation about pregnancy woes.

I was always taught that it’s bad form to assume a woman you don’t know is pregnant. That is true, right? And just in case I’m ever on the receiving end of the question, how does one handle this?

A: Believe me, there is almost no worse conversational gambit than asking a nonpregnant woman when her baby is due. If you start chatting with your seatmate and she happens to mention she’s pregnant, then sure, ask how far along she is, but you just don’t go there unless you are absolutely 1,000 percent positive that she’s pregnant.

Now, if you are not pregnant and someone asks you this question, the gracious thing to do is laugh it off. Don’t slap anybody, even if you’re tempted. A better response, if you want to make the asker squirm, is "Why do you ask?"

Email travel etiquette questions to Lesley Carlin at deartripadvisor@tripadvisor.com.