The icon pack for RCS is added on export to the slideshow.css in case you need icons in your slideshow. The slideshow.css stylesheet icons are referenced differently though so if you have your foundation stylesheet above your slideshow.css, the icons in the slidshow.css will override the foundation.css.
There may be a option to not export the icon pack in RCS settings (like there is in SD3) but I doubt it.
Just edit and remove all icons from that styleseet or just the two that your need to stay unchanged. content: ("\eef0 is the facebook one that is actully youtube icon in the slideshow.css )