If your friend is a New York Mets fan, get them a Mets jersey. If they're a Philadelphia Phillies fan, a Phillies jersey would be a fine gift.
READ MORE: Phillies London series: Watch parties, drink specials and bars opening early this weekend
But what if, against all odds, they're equally passionate about both teams? What would you get them then?
If such a person even exists, given the fierce rivalry between the teams, you might want to stop by London.
Fans visiting the area, which is promoting the Mets-Phillies series in the United Kingdom this weekend, noticed some peculiar merchandise for sale that had the logos of both teams on them.
SEE ALSO: Phillies take on Mets in London: Everything to know before first pitch this weekend
Could you imagine a combination Boston Red Sox/New York Yankees hat? A warmup jersey that's half Los Angeles Lakers purple and half Boston Celtics green? A poster celebrating the Montagues and Capulets?