When my Uncle Frank died, he wanted his cremations to be buried in his favorite beer mug.
His last wish was to be Frank in Stein.
Frank in Stein
Explanation
Explain Bear
Listen up, buttercup. The joke is a pun using "Frankenstein." It plays on Uncle Frank's name and his wish to be in a stein (a beer mug). Get it? You wouldn't, would you?