Full sized bikes are carried (a) on trains that have dedicated bike spaces (b) off-peak on other services. Folding bikes are allowed on any service provided they are folded.
It is generally agreed that displacing people with bikes on peak services isn't acceptable.
Blocking exits isn't acceptable either. It would be reasonable to make a complaint, as promptly as possible.
http://www.irishrail.ie/your_journey...nformation.asp
http://www.railusers.ie/passenger_info/bikes.php