'Silly' is typically used in the context of children or childish things. 'Daft' is used in the context of other, non-childish things or people. 'Picking on somebody' is figurative, and it is where you tease and bother somebody. For example, bullies pick on people. 'Picking at somebody' is literal, and it is where you use your fingers to repeatedly pick things (for example, scabs, hairs, etc.) off somebody. This is not socially acceptable.

I agree with Jemma and Wik on both of these points. 'Picking on' someone means singling someone out for criticism or bullying. For example 'It isn't fair. The teacher's always picking on me. He always blames me for everything, and it's not my fault'. I have never heard of the phrase 'pick at someone'. I've even done a quick check to see if this exists in another variant of English, but it doesn't seem to. The main use for 'pick at' is when we say that someone 'picks at their food'. If you have some food and you don't want to eat it - because you're not hungry or you don't like it - we can say that you 'pick at it'. This means you eat tiny amounts, like a bird pecking with its beak.

daft and silly are very similar, (and either can be used) Though, 'silly' usually refers more to intelligence and 'daft' points towards ridiculousness. Here some synonyms of these words so you can get an idea; daft; synonyms: absurd, preposterous, ridiculous, ludicrous, farcical, laughable silly; synonyms: foolish, stupid, unintelligent, idiotic, brainless, mindless, witless ----------- "picking at somebody" is not correct. (unless there is a bird picking at somebody. Whereas 'picking' is done by the bird's beak.) "picking on somebody" refers to bullying, which is what you were looking for.

-Daft and silly have the same meaning. -Picking on Somebody means bullying another person -Picking at somebody means pestering someone