The c100 knife was added as an unlockable item when you reach colonel 100 in Battlefield 4. This is in reference to the episode Tugg Life where the colonel unlocks his bipod knife.
The bipod knife is available after you reach col. 100 in the dlc final stand
The BFF cast lend their voices as 'easter eggs' in Battlefield 4's campaign.
In Battlefield 4 you can unlock the bipod knife, something that was created by the cast of BFF as a weapon for the col 100 character in the series.
In the battlefield 4 campaign there is an easter egg where you can hear the noob and recon argue about pizza