1) find the youtube clip on youtube.
2) go to the address bar and highlight the address = then copy it either by right clicking ans selecting the copy option or using <ctrl>C
3) go to the topic in CF
4) press the REPLY button (or quote); not quick reply
5) find the youtube option at the top - click on it
6) put the cursor in between the two brackets and "paste" either from the right click option or <ctrl>V