well it's not just local custom since flowers are good for all occasions all over the world :-) But if you ever happen to meet someone nice in this part of the world then this tip can be useful :-)
I'm putting the link for one of local flowers shops so that you can send her/him flowers :)
Master Twardowski is a Polish folklore character, a sorcerer who entered a pact with the Devil. Similar to the figure of Faust in German literature.
Master Twardowski spent some time in the city of Bydgoszcz, where, in his memory, a figure was recently mounted in a window of a tenement, overseeing the Old Town. At 1:13 p.m. and 9:13 p.m. the window opens and Pan Twardowski appears, to the accompaniment of weird music and devilish laughter. He takes a bow, waves his hand, and then disappears. This little show gathers crowds of amused spectators.
There is an impressive crib during Christmas time on the main market square. This is a temporary building, huge and you may enter inside and see the interior. There is a widespread custom of making Christmas cribs in Poland. However, most of them are located in churches. The one in Bydgoszcz is an example of a street crib and was quite interesing.
There are some sculptures of a holy family inside. But the most interesing were alive donkeys. Really funny and it is always great to bring children to see donkeys from a close.
'Forest Quarter' (northern part of Bydgoszcz) is a typical residential district. These blocks of flats were built in 50's and 60's.