Disrespect
Your lame jokes cannot impress women. If you do not know how to treat women, it means you should first learn the basics and only then approach girls. The main thing you are supposed to bear in mind while dealing with people is that they need to feel you respect their opinion and personality. If not, you will be dumped.
Bad hygiene
Take care of yourself. Wash more often and make it your regular habit. See the dentist if you have problems, trim your hair and smell good if you are going on a date.