What's the difference between jam and jelly?
You can't jelly your way into someone's pants.
Listen up, buttercup! The joke is a play on words. "Jam" and "jelly" are types of fruit spreads, but "jelly" sounds like "jelly," which implies being soft or yielding. The punchline suggests you can't use gentleness (or jelly) to seduce someone (get into their pants). It's a bit crude, kinda like your sense of humor.