Yalqun is correct. This slang term is out-of-date. And, I would be very surprised if you ever heard this spoken by an adult. I, too, remember it from high school.

"dis" is slang for "disrespect". Ignoring some one is a form of disrespect or "dissing". We used to use it when I was in high school so it might be a bit out of date by now.

Generally, to" dis "somebody is to show disrespect in some way, so if your friend did not call you, and then disrespected ( dissed) you, when other people were around, I don't think you would like her, and, I imagine, as far as most Chinese were concerned, there would be an issue of" losing face "to consider. This word is very much a new slang word most often used by the younger generation I believe

'Dis' is American slang and means to treat someone with disrespect or to be rude to or insult someone. 'He got dissed ( insulted) by the other guys on the team.' 'Dis' can also mean to criticise something/someone in a way that shows disrespect. 'Don't dis my girlfriend.' It orginates from and is an abbreviation of the verb 'disrespect'. So your sentence means, 'If your friend never called and insulted or criticised you when other people were around, would you still like her?'

Dis the teacher = say that the teacher is rubbish or similar bad stuff Girls dis their boyfriends or husbands when they get together.