By this, I mean have gotten both slime and water poured on their heads, albeit not necessarily on YCTOTV; here's the list that I've gotten so far:

Joanna Garcia
Mandy Moore
Melissa Joan Hart
Amanda Bynes
Jessica Gaynes

Sandra Bullock got slimed.

So did many other actresses; I'm referring to actresses who've gotten both slimed and had water poured on their heads--not even in the latter case necessarily by Nickelodeon.

Dolly Parton is another example.

I LOVE Melissa Joan Hart. I saw her slime clip. When did she get watered?

Alanis Morissette got slimed (at age 11) on YCDTOT, and had a pie fight with her band for her video You Learn.

There's an episode of Xena where they get into a pie fight and Lucy Lawless takes a couple excellent pie hits.

Videos and photos please

Well, both on an episode of Sabrina, and also for the Ice Bucket challenge.

Also Katy Perry....

As Well as Mary kate and Ashley Olsen Also Victoria Justice Many Times even did a photoshoot covered in Slime!