Pratt invited Arnie to join him for a recent child hunger fundraiser online, introducing him as "a pretty important guy."
The Marvel star added, "He is Mr. Universe. He is the Terminator. He's the former Governor of California. He's my father-in-law. My daughter's grandfather. In a word, I better not screw this up or I will be terminated."
But it was Schwarzenegger who messed up, entering the chat and saying, "Hello, Chris Evans."
Realising his error, Arnie quickly added, "Not Chris Evans, sorry. I'm gonna screw up this thing right from the beginning. Chris Pratt. I didn't look at the cue cards the right way. Sorry about that."
Pratt appeared less than pleased, prompting his father-in-law to add, "I mean, I should know your name. I should know your name... That's for sure. You're my favourite son-in-law."
The "Guardians of the Galaxy" star, who married Katherine Schwarzenegger in 2019, added, "I'm your only son-in-law! I better be your favourite."
The rest of Pratt's virtual event went off without a hitch and helped him raise over $615,000 (£451,000) for the non-profit Greater Good. The fundraiser also featured appearances from Jamie Foxx and Robert Downey Jr.
Arnold Schwarzenegger previously said he never thought his daughter Katherine would marry Chris Pratt because she never liked being on the movie sets when she was young. "I said to myself, she would be sick and tired of me dragging them to sets, having them watch me blowing up buildings and killing people. My kids always enjoyed it, but Katherine, she was crying always the first few weeks," Arnie explained.