A face like a bulldog chewing a wasp.

[Bbbananas]

Now I can understand where that expression comes from.
And a face like a slapped @rse - that's pretty obvious what it would look like (red cheeks).
A face that only a mother could love - ahh (ugly).
A face like an unmade bed (wrinkled & creased).
But - a face like the back of a bus??? Don't get that one. How can a face look like any part of the bus - if anything, it would be the front of the bus wouldn't it?

[NoMercy]

How about a face like a warthog, licking p!ss off a stinging nettle?

[MWB]

Maybe because it's dirty?

[MWB]

lmfao nom.