Here's a practical joke that a LARPer
Can play on their friend who's a harper:
Tune her strings each to A,
Then invite her to play
At the Elvenqueen's feast (and then scarper!)

Based on the suggestion: "harp"

LARP stands for Live Action Role-Playing [Game].  LARPers tend to dress in costume and participate in historical recreations or fantasy situations.

And, in case it's not clear from context, "to scarper" means "to flee."