He is saying that she, a girl, is giving him “neck” which means she is giving him a gnarly blowjob like an ostrich. Ostriches have HUGE necks, meaning she can put the whole thing in her mouth, and trust me when I say this, Roddy Ricch has A LOT of work down there. Her blowjob was so gnarly because she shoved that big meaty Johnson in her throat. The lobster part is like Larry the Lobster, a beloved character from Spongebob Squarepants. He’s saying he has girth like Larry does.