I've had a couple of new 'friends' over the past few years that have turned out to be really unpleasant individuals. They shared common 'tactics' early in our 'friendship':
1 Moving too fast with personal revelations, inviting to lunch, etc, a bit like you hear abusive relationships start. Almost a love-bombing.
2 Slightly cagey when trying to pin them down on exactly when these lunches etc would be
3 Ignoring me in crowds, but overly-friendly texts etc.
4 Lots of tales of falling out with other people. It was always the other people's fault, of course
5 Smile that fades in an instant when they don't need to look interested.
6 Quick to pounce on bad things in my life, to add to their arsenal.
I no longer see either of these people. The first one blocked me on FB when I had the temerity to leave where we lived (was obvs no use to her any more). The second I just take a 'smile and wave' to any overtures to meet up.