I'm sure there are some obnoxious people out there, but also I think there is a bit of a social hit resulting directly from the poor functionality. People are often lazy and/or not super tech literate, so for example when someone wants to send a couple pics from an event they'll default to iPhone-only group chat to avoid destroying the quality of the image, rather than using a different sharing mechanism. This is sometimes accompanied by a misunderstanding that Android phones are at fault for the downsampling, when actually it is the iPhone causing the issue and getting away with it due to majority rule.

Additionally, when you first make the switch (at least circa 5 years ago), any iPhone-only group chats you were already in will need to be restarted (with some care taken by each iPhone user involved), otherwise you will not receive those messages because iOS will continue to treat it as an iMessage on others' end. It is very easy to miss out on communications this way, and from there it's not all that hard to fall out of touch with people who weren't closer friends to begin with. Either you need to be proactive or your larger social circle needs to be thoughtful and/or really like you.

So with all these issues, there is a bit of extra work involved for everyone when Android phones are involved. Some circles are so iPhone-heavy already it would be a little awkward to be that guy making the whole chat green. Couple it with a false perception that Android coincides with lower socioeconomic status (obviously not true for certain devices anyway) and it's easy to see shallow people being petty about them. Plus less tech literate circles just accidentally excluding people and you get a real fear of social hurdles.