Probably people telling you it is not a good time to visit because of Songkrahn (Thai New Year.. Water Celebration).
As Said it is a water celebration and things (Farangs mostly) can get out of hand. If you are about during this Period 13th April to 19th April or thereabouts you will get drenched. If you dont like being soaked well dont come then.
Bangkok lasts about 3 days whilst Pattaya lasts for a week.
Me I arrive on the 11th for three weeks I love Songkrahn but dont go mad like some stupid farangs. after all it is a huge wet T shirt competition.... and when the girls get hit with the ice water well !!! LOL