Top 20 Funniest Guest Star Appearances in TV History

From surprise drop-ins to planned cameos, these stars stole the show! Join us as we count down the most hilarious guest appearances that had us rolling on the floor. These brief but brilliant moments showcase celebrities stepping out of their comfort zones to deliver unforgettable comedy gold on our favorite TV shows. Our countdown includes Tilda Swinton in "What We Do in the Shadows," Jon Hamm in "30 Rock," Betty White in "Community," Nathan Lane in "Modern Family," and Robin Williams & Billy Crystal's improvised "Friends" scene! Which guest star made you laugh the hardest? Let us know in the comments below! read more...