1) Worrying about what people are thinking about you on the road is the most dangerous thing you can do. It took me a long time to get over it, but the sudden need to impress, to gain the unspoken respect of, etc. the other riders, pedestrians, or drivers around you will lead you towards bad things: poor judgement and distraction. Focus on you, what you need to do to be safe and have a good time.
2) With respect to braking, at least on my bikes, it’s fairly easy to avoid stoppies by using your bodyweight…or rather NOT using your bodyweight. If you’ve ever watched a “how to stoppie” video, you’ll know that one of the keys is to transfer your bodyweight forward, reducing downward force on the rear wheel and making it easier for the bike to rotate upwards around the front wheel. Don’t want to stoppie? Use your legs to keep your bodyweight off your hands and towards the back of the seat. This is especially hard during heavy braking when you’re being pushed forward. The other thing is to be just a tad more progressive in your squeeze. Just like doing a wheelie requires a quick jerk to get the front wheel off the ground, a stoppie becomes more likely if you squeeze the brake lever fast.