I could use your input on this from a politeness/family politics perspective, guys.
As I've mentioned, FI's twin brother is getting married a month before we are. His FI has been really sweet and invited me to her shower, bachelorette, their daughter's birthday party, etc., even though we are basically strangers.
However...last weekend I got an invite (FB) to the bachelorette. Over 50 girls are invited, and they're renting a party bus, pre-drinking at her place and then bar-hopping for five hours or so. Of these girls, I will know 2 - the bride-to-be, and FI's other brother's GF (assuming she comes - and I barely know her, either).
I have something of a small social phobia anyway, and the idea of being out all night with a bunch of girls I don't know (who all know each other - or at least large groups of each other) is a fairly awful idea for me. And on top of it, I don't really drink and despise the party/bar scene - so this whole scenario is the absolute last thing I would ever want to do with my evening. For the record, FI agrees and says that if he were in my shoes, he wouldn't go. What I'm wondering is: what do you think? Is the fact that I'm attending the bridal shower enough to prove my interest and involvement, or do I really need to attend the bachelorette because this is going to affect our relationship as SILs for the rest of our lives?