The first google hit for clam bump is something that calls itself a pornographic haiku. Pretty sad, since it would be hard to imagine 17 more anodyne syllables:
I / love / clam / bump / ing
I / love / clam/ bump / ing/ some / times
But / not / all / the / time
See how helpfully they separated out the syllables for ease of counting. Why do I have a mental image of whoever wrote that haiku as someone who's a bit of a mouth-breather, possibly given to correcting typos by applying White-Out to their computer screen?
OK: it seems to be a term that's used to refer to lesbian sex, which is what I would have guessed. But yet again, reading the entry and its neighbors in the Urban Dictionary made me feel so contaminated that I had to go wash my hands.
I hate the Urban Dictionary. I think at least half the entries in there are completely spurious, just involving people making stuff up to hoodwink other folks. Reprehensible behavior indeed. Nothing like that would ever happen at a respectable site like wûrd • ē. Right?