Plus One or None?

Whoops - sorry for the delay in writing over the past few days. One of the bridesmaids came into town with her new boyfriend for the long weekend, which leads to today's post inspiration. How are you handling the "+1" portion of your invites?

I have a few great friends with really horribly awful significant others. I'm not talking the 'oh, they're okay' type - I mean, the ones who say offensive things, treat my friends poorly, are rude, and complain incessantly. I like to think of myself as a pretty open and reasonable person, but I'm having a hard time justifying spending $100/person on people I don't really want there, even if it's only a few!

A family friend recently had a wedding where the bride's sister's significant other was disliked by the family and wasn't invited. I feel like that's very harsh, especially for people so close, but can understand it. Nobody wants drama while planning, but you also don't want someone bringing the event down.

Has anyone had a similar dilemma? What was your solution?