Chemistry

Chemistry is short hand for "I'm attracted to you".

When someone says they don't want to date you because there was no chemistry, they mean "I can't imagine having sex with you without a lot of alcohol", but are being polite.

Politeness is a huge mercy, so don't get upset with them.  But if this happens a lot, you may need to lower your expectations of physical beauty, and raise them for deeper things.  That is, stop trying to hit on the hottie with the body but no brain, and look for someone smart enough to want to get into your pants/dress/kilt/mumu, etc.

On the other hand if you keep going on dates where you are the one feeling  'no chemistry', then you may need to start asking out the smoking hot guy/gal.   This goes for women too.  I assure you, any man worth dating will be happy if you make the first move.  But remember that guys that get 8 rejections out of 10 tries are doing pretty good, so don't get discouraged when you are turned down.  Guys are easy, so chances are you will probably only get turned down one out of two tries, not 8 out of 10 - as long as you are asking out people that are 'in your league'.