Usually the exchange of numbers has already taken place prior to the date. At the end of the date is usually when you throw in something like give me a call or I'd like to do this again do you care if I give you a call?
Avoid talking about past relationships on a first date. If you catch him talking about a recent split thats a red light in my book. It can quickly turn into a therapy session and thats not what you want. You want someone who has exchanged the luggage for a balanced life. Talking about a recent split is an indication they aren't quite ready to foster a new relationship. Could be a great new "platonic" friend but on that first date talking about a recent lover is a deal breaker for me.
Someone who plays with their cell and keeps either texting, calling, and answering. They may be sending you a signal by doing that. It's rude as hell but it's as clear as it can get they aren't giving you their complete attention. I have ended a date when this has happened in the past.
How to get out of a bad date? Depends how bad it is. Someone playing on a cell like I said is a good example of ending a date. If you want out of a date try it yourself. If it's boring as hell and the conversation is strained a date like that is manageable. Finish it out but don't say give me a call or lets do this again when the date is over. If you just can't stand the guy and really feel like you can't see the date all the way through be polite, direct, and honest. Just tell them you get the feeling they aren't enjoying the date either so you are going to do both yourself and them a favor and call it a night. Nice meeting you. If you were the one who set up the date pay for it. If they set it up offer to pay half and half the tip. Keep it simple, and get the hell out of there LOL
Go home or a club where your friends are. Roll your eyes and swear you will never do that again and within ten minutes start flirting with a hot guy and exchange numbers and try it all again