The saying goes that you only get one chance to make a first impression, and there are behaviors and traits that can make people take an instant dislike to you.
Sharing too many photos on Facebook
Having too many or too few Facebook friends
Disclosing something extremely personal early on in a relationship
Asking someone questions without talking about yourself at all
Posting a close-up profile photo
Hiding your emotions
Acting too nice
Humblebragging
Getting too nervous
Not smiling
Acting like you don't like someone
Having a hard-to-pronounce name
Name-dropping