While bukkake is the act of multiple men cumming over a kneeling person, the act of gugging comes from all the cum being aimed into said person's mouth, and having them hold it all in their mouth while getting fucked afterwards.
If the person perfects the task, they may, for example, be allowed to cum.
Based off the onomatopoeic sound 'glug' when drinking thick liquids.
"Steve dared this chick to a gugging challenge after we all came on her last night. She had no chance though, she was a screamer."