My MIL is outrageous

My DH's uncle (ok, he's really more like a 1st cousin once removed, but it's a lot easier to just use uncle) is turning 60 soon.

We've been invited to a surprise birthday party for him this weekend.

Yesterday while futilely looking for a present for him, my MIL called. The following is the conversation (or a rough approximation thereof):

MIL: Where are you?

Me: At TJ Maxx looking for a present for "The Birthday Boy" (only the finest ...)

MIL: Well that's why I'm calling. I've arranged for a belly dancer to come to the party.

Me: OH MY GOD!

MIL: I was hoping you might want to go in on it with us and have that be your present too.

Me: OH MY GOD!

MIL: She's from a really good troupe, and will only be dancing for about 10 minutes, it will be fun. "The Birthday Boy" will really like it because it will give him something to talk about for a long time.

Me: OH MY GOD!

So, that's the way she rolls. Every so often I think I've gotten used to her ability to surprise me with something, and then she blows that thought out of the water.

Previous "fun" things have included matching velour leopard print cami-pj's for me and DH's brother's girlfriend one Christmas, and leaving DH and I a bag of sex stuff like games and flavored massage oil in our hotel room the night of our wedding. Her definition of "fun" and mine/DH's are a little bit different. Although we know it's usually based out of a deep-seated desire to make someone happy, we don't always feel comfortable.

Once I've gotten a little alcohol in me I can usually loosen up enough to roll with what's going on, but sober, erm. Not so good. And DH has threatened to not go to the party after hearing about her addition. We may have to make a strategic bathroom break at the appropriate time.

So, am I just a total prude? I know that belly dancers do not equal strippers, but I'm still slightly uncomfortable with this plan. Any suggestions or MIL stories to make me feel better?