This is a self-starting siphon. Submerge it in your friend's drink, and in about a second it will automatically start spilling out the other end. Unlike a normal siphon, you don't need to suck on the end or prime it with water first.

This thing is magic. When showing it to people I've found the more physics they've studied the more surprised they are! Flinn Scientific suggests capillary action is required for the fluid level to rise higher than the container level in the "up hill" part. The capillary action is helpful, but I think momentum alone is enough for the phenomenon. What do you think?

See it in action: https://youtu.be/VaST4ummiUg
More thorough explanation of how it works: https://youtu.be/4SEv_GxAo70

Based on the design suggested by FlinnScientific here (took some trial and error):
https://www.flinnsci.com/globalassets/flinn-scientific/all-free-pdfs/dc10499.pdf

OnShape CAD model:
https://cad.onshape.com/documents/b07bf072535b6507e7963b8e/w/7f50381e76bfccd023bc7222/e/86e868e1153b984ab71a134f

Tips:
Submerge the siphon quickly, ensuring the entire elbow dips below the surface level. Hold it there for a second or two until water flows out the other end. If it doesn't work, blow through one end of the siphon to clear out any trapped water and try again.