Some people also like to show up late for whatever appointments/gatherings that they themselves set the time at. I wonder if they know that they are an annoyance and that it's wrong to waste other people's time.
What about settling on the venue and time? I've had a few experience of ding-donging the whole day emailing back and forth with just 5 girls trying to fix the venue and time. We ended up elsewhere in the end anyway. Some dont like spicy food ler, the location, some got prior engagements la..etc etc etc.
I like to just set the venue/time/date and ask everyone OK or NOT. If not, then all's well, limit the ding-donging and throw in other suggestions. If there is no reaching compromise, then forget it. You can't accomodate to everyone. Someone has to be 'let go'.
And...really why make up stories that you've got other plans when you actually don't. Nobody would say you're a loser. Nobody would laugh at you that you've got nothing to do in the weekends. There's nothing weaker than insecurity.