Tucked In- is a classier way of saying, "We Boned, slayed, tapped, or fucked." Being "Tucked In" by a girl hints towards a more tender or romantic night, and often times the couple performing a "Tuck In" have feelings towards one another. This doesn't mean a worthy "Tuck In" cant be aggressive or describe a one night sex rampage.
Friend- "Bro, what did you and that girl end up doing last night? Did you slay?
You (smiling)- I got tucked in quite nicely.