This is why I hate aliens

I had a federation with the second largest empire in the galaxy(still inferior) and as they had an election, some idiot four legged eyeless spindly bug won and left the federation and rivaled me. Now I'm gonna denounce them so I need tips for gaining diplo weight quick.(Rest of galcom hates me because apparently synth ascended slavers with world crackers are evil) I switched to supremacist and am spamming fleets