I guess s/he isn't technically saying something false, but it is a bit deceptive. Why not just use a more genuine ice-breaker? Compliment someone's tie or shoes or ask if they saw the game last night or...
2. One pretends he or she has an appointment or has something to do in order to end an uncomfortable conversation with someone.
Why make up something specific instead of saying something general instead? "I'm sorry to cut you off, but I really have a lot of work I need to get back to, excuse me." That statement is always true for me, it doesn't hurt people's feelings, and I get on with my day.
3. Someone gives impression as if he is looking at something else when he is actually looking at somebody watch.
4. Someone asks personal questions, as a reply we answer "I don't know".I can't imagine why I would do this. It doesn't have to do with Right Speech in any case. But it sounds devious and probably a bad idea.
I think it depends on the person we are talking to, if we know someone is going to be offended with our respond, we are trying not to offend them. Annoying questions or cultural differences can cause this and the answer such as "I don't know" can come up.I wouldn't do this, either. If I felt like answering, I would. If I didn't, I would decline and be frank about why. I think it's worth noting that we can be firm without violating the fourth precept.
I think there are many reasons, some people have different character such as very straightforward character but other people are not very direct.
As for the first and second reply, complimenting someone when one doesn't want to complimenting or saying " I really have a lot of work " when one doesn't have a lot of work, IMO, is the same thing as lying.