Despite their similarities, Snoopy and Lucy frequently clashed throughout the long run of Peanuts. Whether it was due to Snoopy sniffing in Lucy’s root beer or Lucy insulting Snoopy’s writing, the pair always seemed to find themselves going back and forth. Both characters have bold and often brash personalities, making fights between them unavoidable. They are both stubborn and opinionated, refusing to budge in their ways unless they really prefer a different option. As a result, punches (and dog kisses) have flown in a number of comics.
https://screenrant.com/funniest-peanuts-comics-snoopy-fights-lucy/