Charlie Sheen -- Suck on This Grenade ... and Die.

Charlie Sheen is killing Brooke Mueller with kindness -- at least he really, really wants to -- because he just wished his ex-wife a happy birthday with a special piece of cake (topped with a grenade).

FYI, it's not actually Brooke's birthday (that's in August) but it didn't stop Charlie from writing this message on Twitter, "Happy Bday Brooke. When you're done sucking off the parking lot at Home Depot, why don't ya 'blow' out this candle?"

Now that's love.

Oh yeah, if you recognize the cake ... that's because it's the same cake Charlie got for his recent "Anger Management" party.

The Warlock has returned.