The phrasal verb "geek out" means to get really excited about the small details of a subject. Things that people sometimes "geek out" over include:

• computers
• comic books
• sports statistics

You can explain what someone is interested in with "geek out over ___":

I used to geek out over music equipment.

People also sometimes say "geek out about ___":

Math is a subject that I can really geek out about.

When people "geek out" together in a conversation or an online chat, you use "with":

I love it when I can geek out with other baseball fans.