SUBREDDIT: r/relationships
TITLE: I [18m] need help with my friend [18m]. He makes extremely vulgar jokes about my girlfriend and it's really getting to me.
POST: So I want to start off by saying it is really hard to detect his sarcasm. I know he does it all to bother me but it's getting ridiculous.

Also I'd like to say that my gf doesn't mind and sometimes goes along with them.

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So here's some examples (all said over skype)

"Don't worry man. You get pus and I get mouth. She'll last like 2 minutes before she chokes"

And after I said that was weird

"What are you going to do about it? I'll hold you off with one arm while she sucks me off"

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And tons of other stuff to that extent. Some even to my girlfriend only without me there in the chat (she showed me)

So my question is what can I do. When I said it made me uncomfortable he said to just man up and deal with it. Also what can I say to my gf. She is on the edge. She almost sees why I'm upset but not fully.
TL;DR: 
my friend says really terrible things to me and my gf as jokes. How do I get him to stop and get my gf to see why I'm upset