As soon as I hung up, my friend exclaimed, "How could you possibly talk to your mother that calmly when you're tripping?!" I laughed and told him about the time I had spent the peak of a trip in a Rite-Aid getting heart medication for my ex-boyfriend's mother, without anyone realizing that the two of us were on drugs. And the time that I couldn't figure out how to work the refrigerator while my friend's parents were in the room. And the time that my dad came to pick me up early from a friend's house while I was still tripping, and my phone wasn't working and I knew he was going to be angry that I kept him waiting so long. I survived those things; I was perfectly capable of handling a short phone call from Mom.
For psychonauts, dealing with the "normals" can be terrifying, and cause a lot of anxiety and paranoia which then subsequently affects your trip. However, it's really not as hard as it seems-- unless you're REALLY far-out, you still have perfect control over yourself and can carry off interactions with ease. Actually, I am much better at keeping my shit while I'm on acid than I am while I'm high. It's easy, if you remember a few important things.
1. Don't do anything really weird. Really, this is common sense. No yodeling, no hand-stands in the middle of the highway, and only engage in minimal frolicking if you can help it. Attracting attention is a bad idea. Saying "act natural" is a cliche and often increases anxiety, so don't try too hard-- just draw the line at really silly stuff.
2. Be careful what you say out loud. This is related to the last one, but the verbal element of interaction is a little different from the physical. For example, if you think you see something weird, don't comment on it even if you're relatively sure it's part of actual reality. Never say, "Wow, Mom, do you see that blinking light?" or "Holy fuck, look at that bird!" If someone else comments on it, say "Oh, weird" and go on about your business.
3. Don't let them see your pupils. I realize that trying to hide your eyes can make you paranoid and make you look shifty, but just don't make overly-long eye contact. Busy yourself with your hands, a book, your cell phone, making food, etc. Not too hard to pull off.
4. Remember that strangers don't know what you're like sober. They have nothing to compare your behavior to, so unless you're acting out, like I warned you about in #1, they won't know the difference.
5. Keep conversations as concise as is normal for you. The rules: no rambling, no ranting, no exclamations, no voicing of strong opinions. Be polite and then get on with your life.
6. As a last resort, admit to being high. Or sick. If someone who wouldn't approve of your psychedelic use calls you out on acting strangely or having dilated pupils, admit that you're high (which is less of an offense in most people's minds) and take the consequences for it. They probably won't be that bad. I have never had to resort to this, but I have used the sick excuse. While avoiding long conversations (tip #5) and then skedaddling to my bedroom to hide, I have been asked "What's wrong?" and replied that I was tired because I hadn't slept well the night before due to congestion. Then, when I couldn't sleep that night because of the acid, no one thought it was weird that I took a nap in the afternoon.
The key is to remember that while the world may be very strange to you, no one else can see what you're seeing. Unless you really give it away, they're not going to realize you're tripping. These tips apply whether you're dropping in at the grocery store or having a surprise visit from your grandparents. I hope this dispels some anxiety you psychonauts feel about dealing with sober people, so you can pull off stealth-tripping with less anxiety and more fun.